/*
    * Copyright (C) 2020 Alberto Irurueta Carro (alberto@irurueta.com)
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
    *         http://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package com.irurueta.navigation.inertial.calibration.magnetometer;
  
  import com.irurueta.algebra.AlgebraException;
  import com.irurueta.algebra.Matrix;
  import com.irurueta.algebra.WrongSizeException;
  import com.irurueta.navigation.LockedException;
  import com.irurueta.navigation.NotReadyException;
  import com.irurueta.navigation.frames.CoordinateTransformation;
  import com.irurueta.navigation.frames.FrameType;
  import com.irurueta.navigation.frames.NEDFrame;
  import com.irurueta.navigation.frames.converters.ECEFtoNEDFrameConverter;
  import com.irurueta.navigation.inertial.BodyKinematics;
  import com.irurueta.navigation.inertial.BodyMagneticFluxDensity;
  import com.irurueta.navigation.inertial.calibration.CalibrationException;
  import com.irurueta.navigation.inertial.calibration.MagneticFluxDensityTriad;
  import com.irurueta.navigation.inertial.calibration.StandardDeviationFrameBodyMagneticFluxDensity;
  import com.irurueta.navigation.inertial.estimators.BodyMagneticFluxDensityEstimator;
  import com.irurueta.navigation.inertial.wmm.NEDMagneticFluxDensity;
  import com.irurueta.navigation.inertial.wmm.WMMEarthMagneticFluxDensityEstimator;
  import com.irurueta.navigation.inertial.wmm.WorldMagneticModel;
  import com.irurueta.numerical.fitting.FittingException;
  import com.irurueta.numerical.fitting.LevenbergMarquardtMultiVariateFitter;
  import com.irurueta.numerical.fitting.LevenbergMarquardtMultiVariateFunctionEvaluator;
  import com.irurueta.statistics.MaxIterationsExceededException;
  import com.irurueta.units.MagneticFluxDensity;
  import com.irurueta.units.MagneticFluxDensityConverter;
  import com.irurueta.units.MagneticFluxDensityUnit;
  
  import java.io.IOException;
  import java.util.Collection;
  
  /**
   * Estimates magnetometer soft-iron cross couplings and scaling factors.
   * <p>
   * This calibrator uses an iterative approach to find a minimum least squared error
   * solution.
   * <p>
   * To use this calibrator at least 3 measurements at different known frames must
   * be provided. In other words, magnetometer samples must be obtained at 3
   * different positions or orientations.
   * Notice that frame velocities are ignored by this calibrator.
   * <p>
   * Measured magnetic flux density is assumed to follow the model shown below:
   * <pre>
   *     mBmeas = bm + (I + Mm) * mBtrue + w
   * </pre>
   * Where:
   * - mBmeas is the measured magnetic flux density. This is a 3x1 vector.
   * - bm is magnetometer hard-iron bias. Ideally, on a perfect magnetometer,
   * this should be a 3x1 zero vector.
   * - I is the 3x3 identity matrix.
   * - Mm is the 3x3 soft-iron matrix containing cross-couplings and scaling
   * factors. Ideally, on a perfect magnetometer, this should be a 3x3 zero
   * matrix.
   * - mBtrue is ground-truth magnetic flux density. This is a 3x1 vector.
   * - w is measurement noise. This is a 3x1 vector.
   */
  public class KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator implements
          KnownHardIronAndFrameMagnetometerCalibrator<StandardDeviationFrameBodyMagneticFluxDensity,
                  KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener>,
          MagnetometerNonLinearCalibrator, UnorderedStandardDeviationFrameBodyMagneticFluxDensityMagnetometerCalibrator {
  
      /**
       * Indicates whether by default a common z-axis is assumed for the accelerometer,
       * gyroscope and magnetometer.
       */
      public static final boolean DEFAULT_USE_COMMON_Z_AXIS = false;
  
      /**
       * Required minimum number of measurements.
       */
      public static final int MINIMUM_MEASUREMENTS = 3;
  
      /**
       * Number of unknowns when common z-axis is assumed for the accelerometer,
       * gyroscope and magnetometer.
       */
      private static final int COMMON_Z_AXIS_UNKNOWNS = 6;
  
      /**
       * Number of unknowns for the general case.
       */
      private static final int GENERAL_UNKNOWNS = 9;
  
     /**
      * Levenberg-Marquardt fitter to find a non-linear solution.
      */
     private final LevenbergMarquardtMultiVariateFitter fitter = new LevenbergMarquardtMultiVariateFitter();
 
     /**
      * X-coordinate of known hard-iron bias.
      * This is expressed in Teslas (T).
      */
     private double hardIronX;
 
     /**
      * Y-coordinate of known hard-iron bias.
      * This is expressed in Teslas (T).
      */
     private double hardIronY;
 
     /**
      * Z-coordinate of known hard-iron bias.
      * This is expressed in Teslas (T).
      */
     private double hardIronZ;
 
     /**
      * Initial x scaling factor.
      */
     private double initialSx;
 
     /**
      * Initial y scaling factor.
      */
     private double initialSy;
 
     /**
      * Initial z scaling factor.
      */
     private double initialSz;
 
     /**
      * Initial x-y cross coupling error.
      */
     private double initialMxy;
 
     /**
      * Initial x-z cross coupling error.
      */
     private double initialMxz;
 
     /**
      * Initial y-x cross coupling error.
      */
     private double initialMyx;
 
     /**
      * Initial y-z cross coupling error.
      */
     private double initialMyz;
 
     /**
      * Initial z-x cross coupling error.
      */
     private double initialMzx;
 
     /**
      * Initial z-y cross coupling error.
      */
     private double initialMzy;
 
     /**
      * Contains a collection of body magnetic flux density measurements taken
      * at different frames (positions and orientations) and containing the
      * standard deviation of magnetometer measurements.
      * If a single device magnetometer needs to be calibrated, typically all
      * measurements are taken at the same position, with zero velocity and
      * multiple orientations.
      * However, if we just want to calibrate a given magnetometer model (e.g.
      * obtain an average and less precise calibration for the magnetometer of
      * a given phone model), we could take measurements collected throughout
      * the planet at multiple positions while the phone remains static (e.g.
      * while charging), hence each measurement position will change, velocity
      * will remain zero and orientation will be typically constant at
      * horizontal orientation while the phone remains on a
      * flat surface.
      */
     private Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements;
 
     /**
      * This flag indicates whether z-axis is assumed to be common for accelerometer,
      * gyroscope and magnetometer.
      * When enabled, this eliminates 3 variables from Mm matrix.
      */
     private boolean commonAxisUsed = DEFAULT_USE_COMMON_Z_AXIS;
 
     /**
      * Listener to handle events raised by this calibrator.
      */
     private KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener;
 
     /**
      * Estimated magnetometer soft-iron matrix containing scale factors
      * and cross coupling errors.
      * This is the product of matrix Tm containing cross coupling errors and Km
      * containing scaling factors.
      * So tat:
      * <pre>
      *     Mm = [sx    mxy  mxz] = Tm*Km
      *          [myx   sy   myz]
      *          [mzx   mzy  sz ]
      * </pre>
      * Where:
      * <pre>
      *     Km = [sx 0   0 ]
      *          [0  sy  0 ]
      *          [0  0   sz]
      * </pre>
      * and
      * <pre>
      *     Tm = [1          -alphaXy    alphaXz ]
      *          [alphaYx    1           -alphaYz]
      *          [-alphaZx   alphaZy     1       ]
      * </pre>
      * Hence:
      * <pre>
      *     Mm = [sx    mxy  mxz] = Tm*Km =  [sx             -sy * alphaXy   sz * alphaXz ]
      *          [myx   sy   myz]            [sx * alphaYx   sy              -sz * alphaYz]
      *          [mzx   mzy  sz ]            [-sx * alphaZx  sy * alphaZy    sz           ]
      * </pre>
      * This instance allows any 3x3 matrix however, typically alphaYx, alphaZx and alphaZy
      * are considered to be zero if the accelerometer z-axis is assumed to be the same
      * as the body z-axis. When this is assumed, myx = mzx = mzy = 0 and the Mm matrix
      * becomes upper diagonal:
      * <pre>
      *     Mm = [sx    mxy  mxz]
      *          [0     sy   myz]
      *          [0     0    sz ]
      * </pre>
      * Values of this matrix are unit-less.
      */
     private Matrix estimatedMm;
 
     /**
      * Estimated covariance matrix for estimated parameters.
      */
     private Matrix estimatedCovariance;
 
     /**
      * Estimated chi square value.
      */
     private double estimatedChiSq;
 
     /**
      * Estimated degrees of freedom of chi square value. Degrees of freedom is equal to the number of sampled data
      * minus the number of estimated parameters.
      */
     private int estimatedChiSqDegreesOfFreedom;
 
     /**
      * Estimated reduced chi square value. This is equal to estimated chi square value divided by its degrees of
      * freedom. Ideally this value should be close to 1.0.
      */
     private double estimatedReducedChiSq;
 
     /**
      * Estimated mean square error respect to provided measurements.
      */
     private double estimatedMse;
 
     /**
      * Estimated probability of finding a smaller chi square value expressed as a value between 0.0 and 1.0. The smaller
      * the found chi square value is, the better the fit of the estimated parameters to the actual parameter. Thus, the
      * smaller the chance of finding a smaller chi square value, then the better the estimated fit is.
      */
     private double estimatedP;
 
     /**
      * Estimated measure of quality of estimated fit as a value between 0.0 and 1.0. The larger the quality value is,
      * the better the fit that has been estimated.
      */
     private double estimatedQ;
 
     /**
      * Indicates whether calibrator is running.
      */
     private boolean running;
 
     /**
      * Contains Earth's magnetic model.
      */
     private WorldMagneticModel magneticModel;
 
     /**
      * Constructor.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator() {
     }
 
     /**
      * Constructor.
      *
      * @param listener listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements) {
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      * @param listener     listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(final boolean commonAxisUsed) {
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final boolean commonAxisUsed) {
         this(measurements);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(final WorldMagneticModel magneticModel) {
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param listener      listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final WorldMagneticModel magneticModel,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(listener);
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel) {
         this(measurements);
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param listener      listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, listener);
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel) {
         this(commonAxisUsed);
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed, listener);
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel) {
         this(measurements, commonAxisUsed);
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed, listener);
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param hardIronX x-coordinate of magnetometer hard-iron bias
      *                  expressed in Teslas (T).
      * @param hardIronY y-coordinate of magnetometer hard-iron bias
      *                  expressed in Teslas (T).
      * @param hardIronZ z-coordinate of magnetometer hard-iron bias
      *                  expressed in Teslas (T).
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final double hardIronX, final double hardIronY, final double hardIronZ) {
         try {
             setHardIronCoordinates(hardIronX, hardIronY, hardIronZ);
         } catch (final LockedException ignore) {
             // never happens
         }
     }
 
     /**
      * Constructor.
      *
      * @param hardIronX x-coordinate of magnetometer hard-iron bias
      *                  expressed in Teslas (T).
      * @param hardIronY y-coordinate of magnetometer hard-iron bias
      *                  expressed in Teslas (T).
      * @param hardIronZ z-coordinate of magnetometer hard-iron bias
      *                  expressed in Teslas (T).
      * @param listener  listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(hardIronX, hardIronY, hardIronZ);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      * @param hardIronX    x-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param hardIronY    y-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param hardIronZ    z-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final double hardIronX, final double hardIronY, final double hardIronZ) {
         this(hardIronX, hardIronY, hardIronZ);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      * @param hardIronX    x-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param hardIronY    y-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param hardIronZ    z-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param listener     listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, hardIronX, hardIronY, hardIronZ);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final double hardIronX, final double hardIronY, final double hardIronZ) {
         this(hardIronX, hardIronY, hardIronZ);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final double hardIronX, final double hardIronY, final double hardIronZ,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed, hardIronX, hardIronY, hardIronZ);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final boolean commonAxisUsed, final double hardIronX, final double hardIronY, final double hardIronZ) {
         this(commonAxisUsed, hardIronX, hardIronY, hardIronZ);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed, hardIronX, hardIronY, hardIronZ);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIronX     x-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronY     y-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronZ     z-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ) {
         this(hardIronX, hardIronY, hardIronZ);
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIronX     x-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronY     y-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronZ     z-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param listener      listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(magneticModel, hardIronX, hardIronY, hardIronZ);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIronX     x-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronY     y-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronZ     z-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ) {
         this(hardIronX, hardIronY, hardIronZ);
         this.measurements = measurements;
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIronX     x-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronY     y-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronZ     z-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param listener      listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, magneticModel, hardIronX, hardIronY, hardIronZ);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ) {
         this(magneticModel, hardIronX, hardIronY, hardIronZ);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed, magneticModel, hardIronX, hardIronY, hardIronZ);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ) {
         this(commonAxisUsed, magneticModel, hardIronX, hardIronY, hardIronZ);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed, magneticModel, hardIronX, hardIronY, hardIronZ);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param hardIronX x-coordinate of magnetometer hard-iron bias
      *                  expressed in Teslas (T).
      * @param hardIronY y-coordinate of magnetometer hard-iron bias
      *                  expressed in Teslas (T).
      * @param hardIronZ z-coordinate of magnetometer hard-iron bias
      *                  expressed in Teslas (T).
      * @param initialSx initial x scaling factor.
      * @param initialSy initial y scaling factor.
      * @param initialSz initial z scaling factor.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz) {
         this(hardIronX, hardIronY, hardIronZ);
         try {
             setInitialScalingFactors(initialSx, initialSy, initialSz);
         } catch (final LockedException ignore) {
             // never happens
         }
     }
 
     /**
      * Constructor.
      *
      * @param hardIronX x-coordinate of magnetometer hard-iron bias
      *                  expressed in Teslas (T).
      * @param hardIronY y-coordinate of magnetometer hard-iron bias
      *                  expressed in Teslas (T).
      * @param hardIronZ z-coordinate of magnetometer hard-iron bias
      *                  expressed in Teslas (T).
      * @param initialSx initial x scaling factor.
      * @param initialSy initial y scaling factor.
      * @param initialSz initial z scaling factor.
      * @param listener  listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      * @param hardIronX    x-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param hardIronY    y-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param hardIronZ    z-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param initialSx    initial x scaling factor.
      * @param initialSy    initial y scaling factor.
      * @param initialSz    initial z scaling factor.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz) {
         this(hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      * @param hardIronX    x-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param hardIronY    y-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param hardIronZ    z-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param initialSx    initial x scaling factor.
      * @param initialSy    initial y scaling factor.
      * @param initialSz    initial z scaling factor.
      * @param listener     listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz) {
         this(hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz) {
         this(commonAxisUsed, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIronX     x-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronY     y-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronZ     z-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param initialSx     initial x scaling factor.
      * @param initialSy     initial y scaling factor.
      * @param initialSz     initial z scaling factor.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz) {
         this(hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIronX     x-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronY     y-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronZ     z-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param initialSx     initial x scaling factor.
      * @param initialSy     initial y scaling factor.
      * @param initialSz     initial z scaling factor.
      * @param listener      listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(magneticModel, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIronX     x-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronY     y-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronZ     z-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param initialSx     initial x scaling factor.
      * @param initialSy     initial y scaling factor.
      * @param initialSz     initial z scaling factor.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz) {
         this(magneticModel, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIronX     x-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronY     y-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronZ     z-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param initialSx     initial x scaling factor.
      * @param initialSy     initial y scaling factor.
      * @param initialSz     initial z scaling factor.
      * @param listener      listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, magneticModel, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz) {
         this(magneticModel, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed, magneticModel, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz) {
         this(commonAxisUsed, magneticModel, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed, magneticModel, hardIronX, hardIronY, hardIronZ,
                 initialSx, initialSy, initialSz);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param hardIronX  x-coordinate of magnetometer hard-iron bias
      *                   expressed in Teslas (T).
      * @param hardIronY  y-coordinate of magnetometer hard-iron bias
      *                   expressed in Teslas (T).
      * @param hardIronZ  z-coordinate of magnetometer hard-iron bias
      *                   expressed in Teslas (T).
      * @param initialSx  initial x scaling factor.
      * @param initialSy  initial y scaling factor.
      * @param initialSz  initial z scaling factor.
      * @param initialMxy initial x-y cross coupling error.
      * @param initialMxz initial x-z cross coupling error.
      * @param initialMyx initial y-x cross coupling error.
      * @param initialMyz initial y-z cross coupling error.
      * @param initialMzx initial z-x cross coupling error.
      * @param initialMzy initial z-y cross coupling error.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy) {
         this(hardIronX, hardIronY, hardIronZ);
         try {
             setInitialScalingFactorsAndCrossCouplingErrors(initialSx, initialSy, initialSz,
                     initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
         } catch (final LockedException ignore) {
             // never happens
         }
     }
 
     /**
      * Constructor.
      *
      * @param hardIronX  x-coordinate of magnetometer hard-iron bias
      *                   expressed in Teslas (T).
      * @param hardIronY  y-coordinate of magnetometer hard-iron bias
      *                   expressed in Teslas (T).
      * @param hardIronZ  z-coordinate of magnetometer hard-iron bias
      *                   expressed in Teslas (T).
      * @param initialSx  initial x scaling factor.
      * @param initialSy  initial y scaling factor.
      * @param initialSz  initial z scaling factor.
      * @param initialMxy initial x-y cross coupling error.
      * @param initialMxz initial x-z cross coupling error.
      * @param initialMyx initial y-x cross coupling error.
      * @param initialMyz initial y-z cross coupling error.
      * @param initialMzx initial z-x cross coupling error.
      * @param initialMzy initial z-y cross coupling error.
      * @param listener   listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz, initialMxy, initialMxz, initialMyx,
                 initialMyz, initialMzx, initialMzy);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      * @param hardIronX    x-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param hardIronY    y-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param hardIronZ    z-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param initialSx    initial x scaling factor.
      * @param initialSy    initial y scaling factor.
      * @param initialSz    initial z scaling factor.
      * @param initialMxy   initial x-y cross coupling error.
      * @param initialMxz   initial x-z cross coupling error.
      * @param initialMyx   initial y-x cross coupling error.
      * @param initialMyz   initial y-z cross coupling error.
      * @param initialMzx   initial z-x cross coupling error.
      * @param initialMzy   initial z-y cross coupling error.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy) {
         this(hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz, initialMxy, initialMxz, initialMyx,
                 initialMyz, initialMzx, initialMzy);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      * @param hardIronX    x-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param hardIronY    y-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param hardIronZ    z-coordinate of magnetometer hard-iron bias
      *                     expressed in Teslas (T).
      * @param initialSx    initial x scaling factor.
      * @param initialSy    initial y scaling factor.
      * @param initialSz    initial z scaling factor.
      * @param initialMxy   initial x-y cross coupling error.
      * @param initialMxz   initial x-z cross coupling error.
      * @param initialMyx   initial y-x cross coupling error.
      * @param initialMyz   initial y-z cross coupling error.
      * @param initialMzx   initial z-x cross coupling error.
      * @param initialMzy   initial z-y cross coupling error.
      * @param listener     listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz,
                 initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      * @param initialMxy     initial x-y cross coupling error.
      * @param initialMxz     initial x-z cross coupling error.
      * @param initialMyx     initial y-x cross coupling error.
      * @param initialMyz     initial y-z cross coupling error.
      * @param initialMzx     initial z-x cross coupling error.
      * @param initialMzy     initial z-y cross coupling error.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy) {
         this(hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz, initialMxy, initialMxz, initialMyx,
                 initialMyz, initialMzx, initialMzy);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      * @param initialMxy     initial x-y cross coupling error.
      * @param initialMxz     initial x-z cross coupling error.
      * @param initialMyx     initial y-x cross coupling error.
      * @param initialMyz     initial y-z cross coupling error.
      * @param initialMzx     initial z-x cross coupling error.
      * @param initialMzy     initial z-y cross coupling error.
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz,
                 initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      * @param initialMxy     initial x-y cross coupling error.
      * @param initialMxz     initial x-z cross coupling error.
      * @param initialMyx     initial y-x cross coupling error.
      * @param initialMyz     initial y-z cross coupling error.
      * @param initialMzx     initial z-x cross coupling error.
      * @param initialMzy     initial z-y cross coupling error.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final boolean commonAxisUsed, final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy) {
         this(commonAxisUsed, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz,
                 initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      * @param initialMxy     initial x-y cross coupling error.
      * @param initialMxz     initial x-z cross coupling error.
      * @param initialMyx     initial y-x cross coupling error.
      * @param initialMyz     initial y-z cross coupling error.
      * @param initialMzx     initial z-x cross coupling error.
      * @param initialMzy     initial z-y cross coupling error.
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz,
                 initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIronX     x-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronY     y-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronZ     z-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param initialSx     initial x scaling factor.
      * @param initialSy     initial y scaling factor.
      * @param initialSz     initial z scaling factor.
      * @param initialMxy    initial x-y cross coupling error.
      * @param initialMxz    initial x-z cross coupling error.
      * @param initialMyx    initial y-x cross coupling error.
      * @param initialMyz    initial y-z cross coupling error.
      * @param initialMzx    initial z-x cross coupling error.
      * @param initialMzy    initial z-y cross coupling error.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy) {
         this(hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz,
                 initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIronX     x-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronY     y-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronZ     z-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param initialSx     initial x scaling factor.
      * @param initialSy     initial y scaling factor.
      * @param initialSz     initial z scaling factor.
      * @param initialMxy    initial x-y cross coupling error.
      * @param initialMxz    initial x-z cross coupling error.
      * @param initialMyx    initial y-x cross coupling error.
      * @param initialMyz    initial y-z cross coupling error.
      * @param initialMzx    initial z-x cross coupling error.
      * @param initialMzy    initial z-y cross coupling error.
      * @param listener      listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(magneticModel, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz,
                 initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIronX     x-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronY     y-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronZ     z-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param initialSx     initial x scaling factor.
      * @param initialSy     initial y scaling factor.
      * @param initialSz     initial z scaling factor.
      * @param initialMxy    initial x-y cross coupling error.
      * @param initialMxz    initial x-z cross coupling error.
      * @param initialMyx    initial y-x cross coupling error.
      * @param initialMyz    initial y-z cross coupling error.
      * @param initialMzx    initial z-x cross coupling error.
      * @param initialMzy    initial z-y cross coupling error.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy) {
         this(magneticModel, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz,
                 initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIronX     x-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronY     y-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param hardIronZ     z-coordinate of magnetometer hard-iron bias
      *                      expressed in Teslas (T).
      * @param initialSx     initial x scaling factor.
      * @param initialSy     initial y scaling factor.
      * @param initialSz     initial z scaling factor.
      * @param initialMxy    initial x-y cross coupling error.
      * @param initialMxz    initial x-z cross coupling error.
      * @param initialMyx    initial y-x cross coupling error.
      * @param initialMyz    initial y-z cross coupling error.
      * @param initialMzx    initial z-x cross coupling error.
      * @param initialMzy    initial z-y cross coupling error.
      * @param listener      listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, magneticModel, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz,
                 initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      * @param initialMxy     initial x-y cross coupling error.
      * @param initialMxz     initial x-z cross coupling error.
      * @param initialMyx     initial y-x cross coupling error.
      * @param initialMyz     initial y-z cross coupling error.
      * @param initialMzx     initial z-x cross coupling error.
      * @param initialMzy     initial z-y cross coupling error.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy) {
         this(magneticModel, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz,
                 initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      * @param initialMxy     initial x-y cross coupling error.
      * @param initialMxz     initial x-z cross coupling error.
      * @param initialMyx     initial y-x cross coupling error.
      * @param initialMyz     initial y-z cross coupling error.
      * @param initialMzx     initial z-x cross coupling error.
      * @param initialMzy     initial z-y cross coupling error.
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed, magneticModel, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz,
                 initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      * @param initialMxy     initial x-y cross coupling error.
      * @param initialMxz     initial x-z cross coupling error.
      * @param initialMyx     initial y-x cross coupling error.
      * @param initialMyz     initial y-z cross coupling error.
      * @param initialMzx     initial z-x cross coupling error.
      * @param initialMzy     initial z-y cross coupling error.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy) {
         this(commonAxisUsed, magneticModel, hardIronX, hardIronY, hardIronZ, initialSx, initialSy, initialSz,
                 initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIronX      x-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronY      y-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param hardIronZ      z-coordinate of magnetometer hard-iron bias
      *                       expressed in Teslas (T).
      * @param initialSx      initial x scaling factor.
      * @param initialSy      initial y scaling factor.
      * @param initialSz      initial z scaling factor.
      * @param initialMxy     initial x-y cross coupling error.
      * @param initialMxz     initial x-z cross coupling error.
      * @param initialMyx     initial y-x cross coupling error.
      * @param initialMyz     initial y-z cross coupling error.
      * @param initialMzx     initial z-x cross coupling error.
      * @param initialMzy     initial z-y cross coupling error.
      * @param listener       listener to handle events raised by this calibrator.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel,
             final double hardIronX, final double hardIronY, final double hardIronZ,
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed, magneticModel, hardIronX, hardIronY, hardIronZ,
                 initialSx, initialSy, initialSz, initialMxy, initialMxz, initialMyx,
                 initialMyz, initialMzx, initialMzy);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param hardIron known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(final double[] hardIron) {
         try {
             setHardIron(hardIron);
         } catch (final LockedException ignore) {
             // never happens
         }
     }
 
     /**
      * Constructor.
      *
      * @param hardIron known hard-iron.
      * @param listener listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final double[] hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      * @param hardIron     known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final double[] hardIron) {
         this(hardIron);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      * @param hardIron     known hard-iron.
      * @param listener     listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final double[] hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIron       known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final double[] hardIron) {
         this(hardIron);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIron       known hard-iron.
      * @param listener       listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final double[] hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIron       known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final double[] hardIron) {
         this(commonAxisUsed, hardIron);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIron       known hard-iron.
      * @param listener       listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final double[] hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIron      known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final WorldMagneticModel magneticModel, final double[] hardIron) {
         this(hardIron);
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIron      known hard-iron.
      * @param listener      listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final WorldMagneticModel magneticModel, final double[] hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(magneticModel, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIron      known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel, final double[] hardIron) {
         this(magneticModel, hardIron);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIron      known hard-iron.
      * @param listener      listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel, final double[] hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, magneticModel, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIron       known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel, final double[] hardIron) {
         this(magneticModel, hardIron);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIron       known hard-iron.
      * @param listener       listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel, final double[] hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed, magneticModel, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIron       known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel, final double[] hardIron) {
         this(commonAxisUsed, magneticModel, hardIron);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIron       known hard-iron.
      * @param listener       listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron array does
      *                                  not have length 3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel, final double[] hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed, magneticModel, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param hardIron known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(final Matrix hardIron) {
         try {
             setHardIron(hardIron);
         } catch (final LockedException ignore) {
             // never happens
         }
     }
 
     /**
      * Constructor.
      *
      * @param hardIron known hard-iron.
      * @param listener listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Matrix hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      * @param hardIron     known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final Matrix hardIron) {
         this(hardIron);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      * @param hardIron     known hard-iron.
      * @param listener     listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final Matrix hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIron       known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final Matrix hardIron) {
         this(hardIron);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIron       known hard-iron.
      * @param listener       listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final Matrix hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIron       known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final Matrix hardIron) {
         this(commonAxisUsed, hardIron);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIron       known hard-iron.
      * @param listener       listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final Matrix hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIron      known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final WorldMagneticModel magneticModel, final Matrix hardIron) {
         this(hardIron);
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIron      known hard-iron.
      * @param listener      listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final WorldMagneticModel magneticModel, final Matrix hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(magneticModel, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIron      known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel, final Matrix hardIron) {
         this(magneticModel, hardIron);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIron      known hard-iron.
      * @param listener      listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel, final Matrix hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, magneticModel, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIron       known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel, final Matrix hardIron) {
         this(magneticModel, hardIron);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIron       known hard-iron.
      * @param listener       listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel, final Matrix hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed, magneticModel, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIron       known hard-iron.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel, final Matrix hardIron) {
         this(commonAxisUsed, magneticModel, hardIron);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIron       known hard-iron.
      * @param listener       listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel, final Matrix hardIron,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed, magneticModel, hardIron);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param hardIron  known hard-iron.
      * @param initialMm initial soft-iron matrix containing scale factors
      *                  and cross coupling errors.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Matrix hardIron, final Matrix initialMm) {
         this(hardIron);
         try {
             setInitialMm(initialMm);
         } catch (final LockedException ignore) {
             // never happens
         }
     }
 
     /**
      * Constructor.
      *
      * @param hardIron  known hard-iron.
      * @param initialMm initial soft-iron matrix containing scale factors
      *                  and cross coupling errors.
      * @param listener  listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Matrix hardIron, final Matrix initialMm,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(hardIron, initialMm);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      * @param hardIron     known hard-iron.
      * @param initialMm    initial soft-iron matrix containing scale factors
      *                     and cross coupling errors.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final Matrix hardIron,
             final Matrix initialMm) {
         this(hardIron, initialMm);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements collection of body magnetic flux density measurements with
      *                     standard deviations taken at different frames (positions
      *                     and orientations).
      * @param hardIron     known hard-iron.
      * @param initialMm    initial soft-iron matrix containing scale factors
      *                     and cross coupling errors.
      * @param listener     listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final Matrix hardIron,
             final Matrix initialMm,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, hardIron, initialMm);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIron       known hard-iron.
      * @param initialMm      initial soft-iron matrix containing scale factors
      *                       and cross coupling errors.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final Matrix hardIron, final Matrix initialMm) {
         this(hardIron, initialMm);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIron       known hard-iron.
      * @param initialMm      initial soft-iron matrix containing scale factors
      *                       and cross coupling errors.
      * @param listener       listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final Matrix hardIron, final Matrix initialMm,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed, hardIron, initialMm);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIron       known hard-iron.
      * @param initialMm      initial soft-iron matrix containing scale factors
      *                       and cross coupling errors.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final Matrix hardIron, final Matrix initialMm) {
         this(commonAxisUsed, hardIron, initialMm);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param hardIron       known hard-iron.
      * @param initialMm      initial soft-iron matrix containing scale factors
      *                       and cross coupling errors.
      * @param listener       listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final Matrix hardIron, final Matrix initialMm,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed, hardIron, initialMm);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIron      known hard-iron.
      * @param initialMm     initial soft-iron matrix containing scale factors
      *                      and cross coupling errors.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final WorldMagneticModel magneticModel, final Matrix hardIron, final Matrix initialMm) {
         this(hardIron, initialMm);
         this.magneticModel = magneticModel;
     }
 
     /**
      * Constructor.
      *
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIron      known hard-iron.
      * @param initialMm     initial soft-iron matrix containing scale factors
      *                      and cross coupling errors.
      * @param listener      listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final WorldMagneticModel magneticModel, final Matrix hardIron, final Matrix initialMm,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(magneticModel, hardIron, initialMm);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIron      known hard-iron.
      * @param initialMm     initial soft-iron matrix containing scale factors
      *                      and cross coupling errors.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel, final Matrix hardIron, final Matrix initialMm) {
         this(magneticModel, hardIron, initialMm);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements  collection of body magnetic flux density measurements with
      *                      standard deviations taken at different frames (positions
      *                      and orientations).
      * @param magneticModel Earth's magnetic model. If null, a default model
      *                      will be used instead.
      * @param hardIron      known hard-iron.
      * @param initialMm     initial soft-iron matrix containing scale factors
      *                      and cross coupling errors.
      * @param listener      listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements,
             final WorldMagneticModel magneticModel, final Matrix hardIron, final Matrix initialMm,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, magneticModel, hardIron, initialMm);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIron       known hard-iron.
      * @param initialMm      initial soft-iron matrix containing scale factors
      *                       and cross coupling errors.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel, final Matrix hardIron,
             final Matrix initialMm) {
         this(magneticModel, hardIron, initialMm);
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Constructor.
      *
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIron       known hard-iron.
      * @param initialMm      initial soft-iron matrix containing scale factors
      *                       and cross coupling errors.
      * @param listener       listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final boolean commonAxisUsed, final WorldMagneticModel magneticModel, final Matrix hardIron,
             final Matrix initialMm,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(commonAxisUsed, magneticModel, hardIron, initialMm);
         this.listener = listener;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIron       known hard-iron.
      * @param initialMm      initial soft-iron matrix containing scale factors
      *                       and cross coupling errors.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel, final Matrix hardIron, final Matrix initialMm) {
         this(commonAxisUsed, magneticModel, hardIron, initialMm);
         this.measurements = measurements;
     }
 
     /**
      * Constructor.
      *
      * @param measurements   collection of body magnetic flux density measurements with
      *                       standard deviations taken at different frames (positions
      *                       and orientations).
      * @param commonAxisUsed indicates whether z-axis is assumed to be common
      *                       for the accelerometer, gyroscope and magnetometer.
      * @param magneticModel  Earth's magnetic model. If null, a default model
      *                       will be used instead.
      * @param hardIron       known hard-iron.
      * @param initialMm      initial soft-iron matrix containing scale factors
      *                       and cross coupling errors.
      * @param listener       listener to handle events raised by this calibrator.
      * @throws IllegalArgumentException if provided hard-iron matrix is not
      *                                  3x1 or if soft-iron matrix is not
      *                                  3x3.
      */
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibrator(
             final Collection<StandardDeviationFrameBodyMagneticFluxDensity> measurements, final boolean commonAxisUsed,
             final WorldMagneticModel magneticModel, final Matrix hardIron, final Matrix initialMm,
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener) {
         this(measurements, commonAxisUsed, magneticModel, hardIron, initialMm);
         this.listener = listener;
     }
 
     /**
      * Gets x-coordinate of known magnetometer hard-iron bias.
      * This is expressed in Teslas (T).
      *
      * @return x-coordinate of known magnetometer hard-iron bias.
      */
     @Override
     public double getHardIronX() {
         return hardIronX;
     }
 
     /**
      * Sets x-coordinate of known magnetometer hard-iron bias.
      * This is expressed in Teslas (T).
      *
      * @param hardIronX x coordinate of magnetometer hard-iron.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setHardIronX(final double hardIronX) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.hardIronX = hardIronX;
     }
 
     /**
      * Gets y-coordinate of known magnetometer hard-iron bias.
      * This is expressed in Teslas (T).
      *
      * @return y-coordinate of known magnetometer hard-iron bias.
      */
     @Override
     public double getHardIronY() {
         return hardIronY;
     }
 
     /**
      * Sets y-coordinate of known magnetometer hard-iron bias.
      * This is expressed in Teslas (T).
      *
      * @param hardIronY y coordinate of magnetometer hard-iron.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setHardIronY(final double hardIronY) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.hardIronY = hardIronY;
     }
 
     /**
      * Gets z-coordinate of known magnetometer hard-iron bias.
      * This is expressed in Teslas (T).
      *
      * @return z-coordinate of known magnetometer hard-iron bias.
      */
     @Override
     public double getHardIronZ() {
         return hardIronZ;
     }
 
     /**
      * Sets z-coordinate of known magnetometer hard-iron bias.
      * This is expressed in Teslas (T).
      *
      * @param hardIronZ z coordinate of magnetometer hard-iron.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setHardIronZ(final double hardIronZ) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.hardIronZ = hardIronZ;
     }
 
     /**
      * Gets known x coordinate of magnetometer hard-iron.
      *
      * @return x coordinate of magnetometer hard-iron.
      */
     @Override
     public MagneticFluxDensity getHardIronXAsMagneticFluxDensity() {
         return new MagneticFluxDensity(hardIronX, MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Gets known x coordinate of magnetometer hard-iron.
      *
      * @param result instance where result will be stored.
      */
     @Override
     public void getHardIronXAsMagneticFluxDensity(final MagneticFluxDensity result) {
         result.setValue(hardIronX);
         result.setUnit(MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Sets known x-coordinate of magnetometer hard-iron.
      *
      * @param hardIronX known x-coordinate of magnetometer hard-iron.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setHardIronX(final MagneticFluxDensity hardIronX) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.hardIronX = convertMagneticFluxDensity(hardIronX);
     }
 
     /**
      * Gets known y coordinate of magnetometer hard-iron.
      *
      * @return y coordinate of magnetometer hard-iron.
      */
     @Override
     public MagneticFluxDensity getHardIronYAsMagneticFluxDensity() {
         return new MagneticFluxDensity(hardIronY, MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Gets known y coordinate of magnetometer hard-iron.
      *
      * @param result instance where result will be stored.
      */
     @Override
     public void getHardIronYAsMagneticFluxDensity(final MagneticFluxDensity result) {
         result.setValue(hardIronY);
         result.setUnit(MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Sets known y-coordinate of magnetometer hard-iron.
      *
      * @param hardIronY known y-coordinate of magnetometer hard-iron.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setHardIronY(final MagneticFluxDensity hardIronY) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.hardIronY = convertMagneticFluxDensity(hardIronY);
     }
 
     /**
      * Gets known z coordinate of magnetometer hard-iron.
      *
      * @return z coordinate of magnetometer hard-iron.
      */
     @Override
     public MagneticFluxDensity getHardIronZAsMagneticFluxDensity() {
         return new MagneticFluxDensity(hardIronZ, MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Gets known z coordinate of magnetometer hard-iron.
      *
      * @param result instance where result will be stored.
      */
     @Override
     public void getHardIronZAsMagneticFluxDensity(final MagneticFluxDensity result) {
         result.setValue(hardIronZ);
         result.setUnit(MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Sets known z-coordinate of magnetometer hard-iron.
      *
      * @param hardIronZ known z-coordinate of magnetometer hard-iron.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setHardIronZ(final MagneticFluxDensity hardIronZ) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.hardIronZ = convertMagneticFluxDensity(hardIronZ);
     }
 
     /**
      * Sets known hard-iron bias coordinates of magnetometer expressed
      * in Teslas (T).
      *
      * @param hardIronX x-coordinate of magnetometer hard-iron.
      * @param hardIronY y-coordinate of magnetometer hard-iron.
      * @param hardIronZ z-coordinate of magnetometer hard-iron.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setHardIronCoordinates(
             final double hardIronX, final double hardIronY, final double hardIronZ) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.hardIronX = hardIronX;
         this.hardIronY = hardIronY;
         this.hardIronZ = hardIronZ;
     }
 
     /**
      * Sets known hard-iron coordinates.
      *
      * @param hardIronX x-coordinate of magnetometer hard-iron.
      * @param hardIronY y-coordinate of magnetometer hard-iron.
      * @param hardIronZ z-coordinate of magnetometer hard-iron.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setHardIronCoordinates(
             final MagneticFluxDensity hardIronX, final MagneticFluxDensity hardIronY,
             final MagneticFluxDensity hardIronZ) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.hardIronX = convertMagneticFluxDensity(hardIronX);
         this.hardIronY = convertMagneticFluxDensity(hardIronY);
         this.hardIronZ = convertMagneticFluxDensity(hardIronZ);
     }
 
     /**
      * Gets known hard-iron.
      *
      * @return known hard-iron.
      */
     @Override
     public MagneticFluxDensityTriad getHardIronAsTriad() {
         return new MagneticFluxDensityTriad(MagneticFluxDensityUnit.TESLA, hardIronX, hardIronY, hardIronZ);
     }
 
     /**
      * Gets known hard-iron.
      *
      * @param result instance where result will be stored.
      */
     @Override
     public void getHardIronAsTriad(final MagneticFluxDensityTriad result) {
         result.setValueCoordinatesAndUnit(hardIronX, hardIronY, hardIronZ, MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Sets known hard-iron.
      *
      * @param hardIron hard-iron to be set.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setHardIron(final MagneticFluxDensityTriad hardIron) throws LockedException {
         if (running) {
             throw new LockedException();
         }
 
         hardIronX = convertMagneticFluxDensity(hardIron.getValueX(), hardIron.getUnit());
         hardIronY = convertMagneticFluxDensity(hardIron.getValueY(), hardIron.getUnit());
         hardIronZ = convertMagneticFluxDensity(hardIron.getValueZ(), hardIron.getUnit());
     }
 
     /**
      * Gets initial x scaling factor.
      *
      * @return initial x scaling factor.
      */
     @Override
     public double getInitialSx() {
         return initialSx;
     }
 
     /**
      * Sets initial x scaling factor.
      *
      * @param initialSx initial x scaling factor.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialSx(final double initialSx) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialSx = initialSx;
     }
 
     /**
      * Gets initial y scaling factor.
      *
      * @return initial y scaling factor.
      */
     @Override
     public double getInitialSy() {
         return initialSy;
     }
 
     /**
      * Sets initial y scaling factor.
      *
      * @param initialSy initial y scaling factor.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialSy(final double initialSy) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialSy = initialSy;
     }
 
     /**
      * Gets initial z scaling factor.
      *
      * @return initial z scaling factor.
      */
     @Override
     public double getInitialSz() {
         return initialSz;
     }
 
     /**
      * Sets initial z scaling factor.
      *
      * @param initialSz initial z scaling factor.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialSz(final double initialSz) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialSz = initialSz;
     }
 
     /**
      * Gets initial x-y cross coupling error.
      *
      * @return initial x-y cross coupling error.
      */
     @Override
     public double getInitialMxy() {
         return initialMxy;
     }
 
     /**
      * Sets initial x-y cross coupling error.
      *
      * @param initialMxy initial x-y cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialMxy(final double initialMxy) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMxy = initialMxy;
     }
 
     /**
      * Gets initial x-z cross coupling error.
      *
      * @return initial x-z cross coupling error.
      */
     @Override
     public double getInitialMxz() {
         return initialMxz;
     }
 
     /**
      * Sets initial x-z cross coupling error.
      *
      * @param initialMxz initial x-z cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialMxz(final double initialMxz) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMxz = initialMxz;
     }
 
     /**
      * Gets initial y-x cross coupling error.
      *
      * @return initial y-x cross coupling error.
      */
     @Override
     public double getInitialMyx() {
         return initialMyx;
     }
 
     /**
      * Sets initial y-x cross coupling error.
      *
      * @param initialMyx initial y-x cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialMyx(final double initialMyx) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMyx = initialMyx;
     }
 
     /**
      * Gets initial y-z cross coupling error.
      *
      * @return initial y-z cross coupling error.
      */
     @Override
     public double getInitialMyz() {
         return initialMyz;
     }
 
     /**
      * Sets initial y-z cross coupling error.
      *
      * @param initialMyz initial y-z cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialMyz(final double initialMyz) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMyz = initialMyz;
     }
 
     /**
      * Gets initial z-x cross coupling error.
      *
      * @return initial z-x cross coupling error.
      */
     @Override
     public double getInitialMzx() {
         return initialMzx;
     }
 
     /**
      * Sets initial z-x cross coupling error.
      *
      * @param initialMzx initial z-x cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialMzx(final double initialMzx) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMzx = initialMzx;
     }
 
     /**
      * Gets initial z-y cross coupling error.
      *
      * @return initial z-y cross coupling error.
      */
     @Override
     public double getInitialMzy() {
         return initialMzy;
     }
 
     /**
      * Sets initial z-y cross coupling error.
      *
      * @param initialMzy initial z-y cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialMzy(final double initialMzy) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMzy = initialMzy;
     }
 
     /**
      * Sets initial scaling factors.
      *
      * @param initialSx initial x scaling factor.
      * @param initialSy initial y scaling factor.
      * @param initialSz initial z scaling factor.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialScalingFactors(
             final double initialSx, final double initialSy, final double initialSz) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialSx = initialSx;
         this.initialSy = initialSy;
         this.initialSz = initialSz;
     }
 
     /**
      * Sets initial cross coupling errors.
      *
      * @param initialMxy initial x-y cross coupling error.
      * @param initialMxz initial x-z cross coupling error.
      * @param initialMyx initial y-x cross coupling error.
      * @param initialMyz initial y-z cross coupling error.
      * @param initialMzx initial z-x cross coupling error.
      * @param initialMzy initial z-y cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialCrossCouplingErrors(
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.initialMxy = initialMxy;
         this.initialMxz = initialMxz;
         this.initialMyx = initialMyx;
         this.initialMyz = initialMyz;
         this.initialMzx = initialMzx;
         this.initialMzy = initialMzy;
     }
 
     /**
      * Sets initial scaling factors and cross coupling errors.
      *
      * @param initialSx  initial x scaling factor.
      * @param initialSy  initial y scaling factor.
      * @param initialSz  initial z scaling factor.
      * @param initialMxy initial x-y cross coupling error.
      * @param initialMxz initial x-z cross coupling error.
      * @param initialMyx initial y-x cross coupling error.
      * @param initialMyz initial y-z cross coupling error.
      * @param initialMzx initial z-x cross coupling error.
      * @param initialMzy initial z-y cross coupling error.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setInitialScalingFactorsAndCrossCouplingErrors(
             final double initialSx, final double initialSy, final double initialSz,
             final double initialMxy, final double initialMxz, final double initialMyx,
             final double initialMyz, final double initialMzx, final double initialMzy) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         setInitialScalingFactors(initialSx, initialSy, initialSz);
         setInitialCrossCouplingErrors(initialMxy, initialMxz, initialMyx, initialMyz, initialMzx, initialMzy);
     }
 
     /**
      * Gets known hard-iron bias as an array.
      * Array values are expressed in Teslas (T).
      *
      * @return array containing coordinates of initial bias.
      */
     @Override
     public double[] getHardIron() {
         final var result = new double[BodyMagneticFluxDensity.COMPONENTS];
         getHardIron(result);
         return result;
     }
 
     /**
      * Gets known hard-iron bias as an array.
      * Array values are expressed in Teslas (T).
      *
      * @param result instance where result data will be copied to.
      * @throws IllegalArgumentException if provided array does not have
      *                                  length 3.
      */
     @Override
     public void getHardIron(final double[] result) {
         if (result.length != BodyMagneticFluxDensity.COMPONENTS) {
             throw new IllegalArgumentException();
         }
         result[0] = hardIronX;
         result[1] = hardIronY;
         result[2] = hardIronZ;
     }
 
     /**
      * Sets known hard-iron bias as an array.
      * Array values are expressed in Teslas (T).
      *
      * @param hardIron known hard-iron bias.
      * @throws LockedException          if calibrator is currently running.
      * @throws IllegalArgumentException if provided array does not have
      *                                  length 3.
      */
     @Override
     public void setHardIron(final double[] hardIron) throws LockedException {
         if (running) {
             throw new LockedException();
         }
 
         if (hardIron.length != BodyMagneticFluxDensity.COMPONENTS) {
             throw new IllegalArgumentException();
         }
         hardIronX = hardIron[0];
         hardIronY = hardIron[1];
         hardIronZ = hardIron[2];
     }
 
     /**
      * Gets known hard-iron bias as a column matrix.
      *
      * @return hard-iron bias as a column matrix.
      */
     @Override
     public Matrix getHardIronMatrix() {
         Matrix result;
         try {
             result = new Matrix(BodyMagneticFluxDensity.COMPONENTS, 1);
             getHardIronMatrix(result);
         } catch (final WrongSizeException ignore) {
             // never happens
             result = null;
         }
         return result;
     }
 
     /**
      * Gets known hard-iron bias as a column matrix.
      *
      * @param result instance where result data will be copied to.
      * @throws IllegalArgumentException if provided matrix is not 3x1.
      */
     @Override
     public void getHardIronMatrix(final Matrix result) {
         if (result.getRows() != BodyMagneticFluxDensity.COMPONENTS || result.getColumns() != 1) {
             throw new IllegalArgumentException();
         }
         result.setElementAtIndex(0, hardIronX);
         result.setElementAtIndex(1, hardIronY);
         result.setElementAtIndex(2, hardIronZ);
     }
 
     /**
      * Sets known hard-iron bias.
      *
      * @param hardIron magnetometer hard-iron bias to be set.
      * @throws LockedException          if calibrator is currently running.
      * @throws IllegalArgumentException if provided matrix is not 3x1.
      */
     @Override
     public void setHardIron(final Matrix hardIron) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         if (hardIron.getRows() != BodyMagneticFluxDensity.COMPONENTS || hardIron.getColumns() != 1) {
             throw new IllegalArgumentException();
         }
 
         hardIronX = hardIron.getElementAtIndex(0);
         hardIronY = hardIron.getElementAtIndex(1);
         hardIronZ = hardIron.getElementAtIndex(2);
     }
 
     /**
      * Gets initial scale factors and cross coupling errors matrix.
      *
      * @return initial scale factors and cross coupling errors matrix.
      */
     @Override
     public Matrix getInitialMm() {
         Matrix result;
         try {
             result = new Matrix(BodyMagneticFluxDensity.COMPONENTS, BodyMagneticFluxDensity.COMPONENTS);
             getInitialMm(result);
         } catch (final WrongSizeException ignore) {
             // never happens
             result = null;
         }
         return result;
     }
 
     /**
      * Gets initial scale factors and cross coupling errors matrix.
      *
      * @param result instance where data will be stored.
      * @throws IllegalArgumentException if provided matrix is not 3x3.
      */
     @Override
     public void getInitialMm(final Matrix result) {
         if (result.getRows() != BodyKinematics.COMPONENTS || result.getColumns() != BodyKinematics.COMPONENTS) {
             throw new IllegalArgumentException();
         }
         result.setElementAtIndex(0, initialSx);
         result.setElementAtIndex(1, initialMyx);
         result.setElementAtIndex(2, initialMzx);
 
         result.setElementAtIndex(3, initialMxy);
         result.setElementAtIndex(4, initialSy);
         result.setElementAtIndex(5, initialMzy);
 
         result.setElementAtIndex(6, initialMxz);
         result.setElementAtIndex(7, initialMyz);
         result.setElementAtIndex(8, initialSz);
     }
 
     /**
      * Sets initial scale factors and cross coupling errors matrix.
      *
      * @param initialMm initial scale factors and cross coupling errors matrix.
      * @throws IllegalArgumentException if provided matrix is not 3x3.
      * @throws LockedException          if calibrator is currently running.
      */
     @Override
     public void setInitialMm(final Matrix initialMm) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         if (initialMm.getRows() != BodyKinematics.COMPONENTS || initialMm.getColumns() != BodyKinematics.COMPONENTS) {
             throw new IllegalArgumentException();
         }
 
         initialSx = initialMm.getElementAtIndex(0);
         initialMyx = initialMm.getElementAtIndex(1);
         initialMzx = initialMm.getElementAtIndex(2);
 
         initialMxy = initialMm.getElementAtIndex(3);
         initialSy = initialMm.getElementAtIndex(4);
         initialMzy = initialMm.getElementAtIndex(5);
 
         initialMxz = initialMm.getElementAtIndex(6);
         initialMyz = initialMm.getElementAtIndex(7);
         initialSz = initialMm.getElementAtIndex(8);
     }
 
     /**
      * Gets a collection of body magnetic flux density measurements taken at different
      * frames (positions, orientations and velocities).
      * If a single device IMU needs to be calibrated, typically all measurements are
      * taken at the same position, with zero velocity and multiple orientations.
      * However, if we just want to calibrate a given IMU model (e.g. obtain
      * an average and less precise calibration for the IMU of a given phone model),
      * we could take measurements collected throughout the planet at multiple positions
      * while the phone remains static (e.g. while charging), hence each measurement
      * position will change, velocity will remain zero and orientation will be
      * typically constant at horizontal orientation while the phone remains on a
      * flat surface.
      *
      * @return a collection of body magnetic flux density measurements taken at different
      * frames (positions, orientations and velocities).
      */
     @Override
     public Collection<StandardDeviationFrameBodyMagneticFluxDensity> getMeasurements() {
         return measurements;
     }
 
     /**
      * Sets a collection of body magnetic flux density measurements taken at different
      * frames (positions, orientations and velocities).
      * If a single device IMU needs to be calibrated, typically all measurements are
      * taken at the same position, with zero velocity and multiple orientations.
      * However, if we just want to calibrate the a given IMU model (e.g. obtain
      * an average and less precise calibration for the IMU of a given phone model),
      * we could take measurements collected throughout the planet at multiple positions
      * while the phone remains static (e.g. while charging), hence each measurement
      * position will change, velocity will remain zero and orientation will be
      * typically constant at horizontal orientation while the phone remains on a
      * flat surface.
      *
      * @param measurements collection of body magnetic flux density measurements
      *                     taken at different frames (positions, orientations
      *                     and velocities).
      * @throws LockedException if estimator is currently running.
      */
     @Override
     public void setMeasurements(
             final Collection<? extends StandardDeviationFrameBodyMagneticFluxDensity> measurements)
             throws LockedException {
         if (running) {
             throw new LockedException();
         }
         //noinspection unchecked
         this.measurements = (Collection<StandardDeviationFrameBodyMagneticFluxDensity>) measurements;
     }
 
     /**
      * Indicates the type of measurement used by this calibrator.
      *
      * @return type of measurement used by this calibrator.
      */
     @Override
     public MagnetometerCalibratorMeasurementType getMeasurementType() {
         return MagnetometerCalibratorMeasurementType.STANDARD_DEVIATION_FRAME_BODY_MAGNETIC_FLUX_DENSITY;
     }
 
     /**
      * Indicates whether this calibrator requires ordered measurements in a
      * list or not.
      *
      * @return true if measurements must be ordered, false otherwise.
      */
     @Override
     public boolean isOrderedMeasurementsRequired() {
         return false;
     }
 
     /**
      * Indicates whether this calibrator requires quality scores for each
      * measurement or not.
      *
      * @return true if quality scores are required, false otherwise.
      */
     @Override
     public boolean isQualityScoresRequired() {
         return false;
     }
 
     /**
      * Indicates whether z-axis is assumed to be common for accelerometer,
      * gyroscope and magnetometer.
      * When enabled, this eliminates 3 variables from Mm (soft-iron) matrix.
      *
      * @return true if z-axis is assumed to be common for accelerometer,
      * gyroscope and magnetometer, false otherwise.
      */
     @Override
     public boolean isCommonAxisUsed() {
         return commonAxisUsed;
     }
 
     /**
      * Specifies whether z-axis is assumed to be common for accelerometer and
      * gyroscope.
      * When enabled, this eliminates 3 variables from Mm matrix.
      *
      * @param commonAxisUsed true if z-axis is assumed to be common for
      *                       accelerometer, gyroscope and magnetometer, false
      *                       otherwise.
      * @throws LockedException if estimator is currently running.
      */
     @Override
     public void setCommonAxisUsed(final boolean commonAxisUsed) throws LockedException {
         if (running) {
             throw new LockedException();
         }
 
         this.commonAxisUsed = commonAxisUsed;
     }
 
     /**
      * Gets listener to handle events raised by this calibrator.
      *
      * @return listener to handle events raised by this calibrator.
      */
     @Override
     public KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener getListener() {
         return listener;
     }
 
     /**
      * Sets listener to handle events raised by this calibrator.
      *
      * @param listener listener to handle events raised by this calibrator.
      * @throws LockedException if calibrator is currently running.
      */
     @Override
     public void setListener(
             final KnownHardIronAndFrameMagnetometerNonLinearLeastSquaresCalibratorListener listener)
             throws LockedException {
         if (running) {
             throw new LockedException();
         }
 
         this.listener = listener;
     }
 
     /**
      * Gets minimum number of required measurements.
      *
      * @return minimum number of required measurements.
      */
     @Override
     public int getMinimumRequiredMeasurements() {
         return MINIMUM_MEASUREMENTS;
     }
 
     /**
      * Indicates whether calibrator is ready to start the estimator.
      *
      * @return true if calibrator is ready, false otherwise.
      */
     @Override
     public boolean isReady() {
         return measurements != null && measurements.size() >= MINIMUM_MEASUREMENTS;
     }
 
     /**
      * Indicates whether calibrator is currently running or no.
      *
      * @return true if calibrator is running, false otherwise.
      */
     @Override
     public boolean isRunning() {
         return running;
     }
 
     /**
      * Gets Earth's magnetic model.
      *
      * @return Earth's magnetic model or null if not provided.
      */
     public WorldMagneticModel getMagneticModel() {
         return magneticModel;
     }
 
     /**
      * Sets Earth's magnetic model.
      *
      * @param magneticModel Earth's magnetic model to be set.
      * @throws LockedException if calibrator is currently running.
      */
     public void setMagneticModel(final WorldMagneticModel magneticModel) throws LockedException {
         if (running) {
             throw new LockedException();
         }
         this.magneticModel = magneticModel;
     }
 
     /**
      * Estimates magnetometer calibration parameters containing scale factors
      * and cross-coupling errors.
      *
      * @throws LockedException      if calibrator is currently running.
      * @throws NotReadyException    if calibrator is not ready.
      * @throws CalibrationException if calibration fails for numerical reasons.
      */
     @Override
     public void calibrate() throws LockedException, NotReadyException, CalibrationException {
         if (running) {
             throw new LockedException();
         }
 
         if (!isReady()) {
             throw new NotReadyException();
         }
 
         try {
             running = true;
 
             if (listener != null) {
                 listener.onCalibrateStart(this);
             }
 
             if (commonAxisUsed) {
                 calibrateCommonAxis();
             } else {
                 calibrateGeneral();
             }
 
             if (listener != null) {
                 listener.onCalibrateEnd(this);
             }
 
         } catch (final AlgebraException | FittingException | com.irurueta.numerical.NotReadyException | IOException e) {
             throw new CalibrationException(e);
         } finally {
             running = false;
         }
     }
 
     /**
      * Gets estimated magnetometer soft-iron matrix containing scale factors
      * and cross coupling errors.
      * This is the product of matrix Tm containing cross coupling errors and Km
      * containing scaling factors.
      * So tat:
      * <pre>
      *     Mm = [sx    mxy  mxz] = Tm*Km
      *          [myx   sy   myz]
      *          [mzx   mzy  sz ]
      * </pre>
      * Where:
      * <pre>
      *     Km = [sx 0   0 ]
      *          [0  sy  0 ]
      *          [0  0   sz]
      * </pre>
      * and
      * <pre>
      *     Tm = [1          -alphaXy    alphaXz ]
      *          [alphaYx    1           -alphaYz]
      *          [-alphaZx   alphaZy     1       ]
      * </pre>
      * Hence:
      * <pre>
      *     Mm = [sx    mxy  mxz] = Tm*Km =  [sx             -sy * alphaXy   sz * alphaXz ]
      *          [myx   sy   myz]            [sx * alphaYx   sy              -sz * alphaYz]
      *          [mzx   mzy  sz ]            [-sx * alphaZx  sy * alphaZy    sz           ]
      * </pre>
      * This instance allows any 3x3 matrix however, typically alphaYx, alphaZx and alphaZy
      * are considered to be zero if the accelerometer z-axis is assumed to be the same
      * as the body z-axis. When this is assumed, myx = mzx = mzy = 0 and the Mm matrix
      * becomes upper diagonal:
      * <pre>
      *     Mm = [sx    mxy  mxz]
      *          [0     sy   myz]
      *          [0     0    sz ]
      * </pre>
      * Values of this matrix are unit-less.
      *
      * @return estimated magnetometer soft-iron scale factors and cross coupling errors,
      * or null if not available.
      */
     @Override
     public Matrix getEstimatedMm() {
         return estimatedMm;
     }
 
     /**
      * Gets estimated x-axis scale factor.
      *
      * @return estimated x-axis scale factor or null if not available.
      */
     @Override
     public Double getEstimatedSx() {
         return estimatedMm != null ? estimatedMm.getElementAt(0, 0) : null;
     }
 
     /**
      * Gets estimated y-axis scale factor.
      *
      * @return estimated y-axis scale factor or null if not available.
      */
     @Override
     public Double getEstimatedSy() {
         return estimatedMm != null ? estimatedMm.getElementAt(1, 1) : null;
     }
 
     /**
      * Gets estimated z-axis scale factor.
      *
      * @return estimated z-axis scale factor or null if not available.
      */
     @Override
     public Double getEstimatedSz() {
         return estimatedMm != null ? estimatedMm.getElementAt(2, 2) : null;
     }
 
     /**
      * Gets estimated x-y cross-coupling error.
      *
      * @return estimated x-y cross-coupling error or null if not available.
      */
     @Override
     public Double getEstimatedMxy() {
         return estimatedMm != null ? estimatedMm.getElementAt(0, 1) : null;
     }
 
     /**
      * Gets estimated x-z cross-coupling error.
      *
      * @return estimated x-z cross-coupling error or null if not available.
      */
     @Override
     public Double getEstimatedMxz() {
         return estimatedMm != null ? estimatedMm.getElementAt(0, 2) : null;
     }
 
     /**
      * Gets estimated y-x cross-coupling error.
      *
      * @return estimated y-x cross-coupling error or null if not available.
      */
     @Override
     public Double getEstimatedMyx() {
         return estimatedMm != null ? estimatedMm.getElementAt(1, 0) : null;
     }
 
     /**
      * Gets estimated y-z cross-coupling error.
      *
      * @return estimated y-z cross-coupling error or null if not available.
      */
     @Override
     public Double getEstimatedMyz() {
         return estimatedMm != null ? estimatedMm.getElementAt(1, 2) : null;
     }
 
     /**
      * Gets estimated z-x cross-coupling error.
      *
      * @return estimated z-x cross-coupling error or null if not available.
      */
     @Override
     public Double getEstimatedMzx() {
         return estimatedMm != null ? estimatedMm.getElementAt(2, 0) : null;
     }
 
     /**
      * Gets estimated z-y cross-coupling error.
      *
      * @return estimated z-y cross-coupling error or null if not available.
      */
     @Override
     public Double getEstimatedMzy() {
         return estimatedMm != null ? estimatedMm.getElementAt(2, 1) : null;
     }
 
     /**
      * Gets estimated covariance matrix for estimated calibration parameters.
      * Diagonal elements of the matrix contains variance for the following
      * parameters (following indicated order): sx, sy, sz, mxy, mxz, myx,
      * myz, mzx, mzy.
      *
      * @return estimated covariance matrix for estimated position.
      */
     @Override
     public Matrix getEstimatedCovariance() {
         return estimatedCovariance;
     }
 
     /**
      * Gets estimated chi square value.
      *
      * @return estimated chi square value.
      */
     @Override
     public double getEstimatedChiSq() {
         return estimatedChiSq;
     }
 
     /**
      * Gets estimated chi square degrees of freedom. Degrees of freedom is equal to the number of sampled data minus the
      * number of estimated parameters.
      *
      * @return estimated degrees of freedom of chi square value
      */
     @Override
     public int getEstimatedChiSqDegreesOfFreedom() {
         return estimatedChiSqDegreesOfFreedom;
     }
 
     /**
      * Gets estimated reduced chi square value. This is equal to estimated chi square value divided by its degrees of
      * freedom. Ideally this value should be close to 1.0, indicating that fit is optimal.
      * A value larger than 1.0 indicates that fit is not good or noise has been underestimated, and a value smaller than
      * 1.0 indicates that there is overfitting or noise has been overestimated.
      *
      * @return estimated reduced chi square value
      */
     @Override
     public double getEstimatedReducedChiSq() {
         return estimatedReducedChiSq;
     }
 
     /**
      * Gets estimated mean square error respect to provided measurements.
      *
      * @return estimated mean square error respect to provided measurements.
      */
     @Override
     public double getEstimatedMse() {
         return estimatedMse;
     }
 
     /**
      * Gets estimated probability of finding a smaller chi square value expressed as a value between 0.0 and 1.0. The
      * smaller the found chi square value is, the better the fit of the estimated parameters to the actual parameter.
      * Thus, the smaller the chance of finding a smaller chi square value, then the better the estimated fit is.
      *
      * @return estimated probability of finding a smaller chi square value.
      */
     @Override
     public double getEstimatedP() {
         return estimatedP;
     }
 
     /**
      * Gets estimated measure of quality of estimated fit as a value between 0.0 and 1.0. The larger the quality value
      * is, the better the fit that has been estimated.
      *
      * @return estimated measure of quality of estimated fit.
      */
     @Override
     public double getEstimatedQ() {
         return estimatedQ;
     }
 
     /**
      * Internal method to perform calibration when common z-axis is assumed for both
      * the accelerometer and gyroscope.
      *
      * @throws AlgebraException                         if there are numerical errors.
      * @throws FittingException                         if no convergence to solution is found.
      * @throws com.irurueta.numerical.NotReadyException if fitter is not ready.
      * @throws IOException                              if world magnetic model cannot be loaded.
      */
     private void calibrateCommonAxis() throws AlgebraException, FittingException,
             com.irurueta.numerical.NotReadyException, IOException {
         // The accelerometer model is:
         // mBmeas = ba + (I + Ma) * mBtrue + w
 
         // Ideally a least squares solution tries to minimize noise component, so:
         // mBmeas = ba + (I + Ma) * mBtrue
 
         // Hence:
         // [mBmeasx] = [bx] + ( [1  0   0] + [sx    mxy mxz])   [mBtruex]
         // [mBmeasy] = [by]     [0  1   0]   [myx   sy  myz]    [mBtruey]
         // [mBmeasz] = [bz]     [0  0   1]   [mzx   mzy sz ]    [mBtruez]
 
         // where myx = mzx = mzy = 0
 
         // Hence:
         // [mBmeasx] = [bx] + ( [1  0   0] + [sx    mxy mxz])   [mBtruex]
         // [mBmeasy] = [by]     [0  1   0]   [0     sy  myz]    [mBtruey]
         // [mBmeasz] = [bz]     [0  0   1]   [0     0   sz ]    [mBtruez]
 
         // [mBmeasx] = [bx] +   [1+sx   mxy     mxz ][mBtruex]
         // [mBmeasy]   [by]     [0      1+sy    myz ][mBtruey]
         // [mBmeasz]   [bz]     [0      0       1+sz][mBtruez]
 
         // mBmeasx = bx + (1+sx) * mBtruex + mxy * mBtruey + mxz * mBtruez
         // mBmeasy = by + (1+sy) * mBtruey + myz * mBtruez
         // mBmeasz = bz + (1+sz) * mBtruez
 
         // Where the unknowns are: sx, sy, sz, mxy mxz, myz
         // Reordering:
         // mBmeasx = bx + mBtruex + sx * mBtruex + mxy * mBtruey + mxz * mBtruez
         // mBmeasy = by + mBtruey + sy * mBtruey + myz * mBtruez
         // mBmeasz = bz + mBtruez + sz * mBtruez
 
         // mBmeasx - mBtruex - bx = sx * mBtruex + mxy * mBtruey + mxz * mBtruez
         // mBmeasy - mBtruey - by = sy * mBtruey + myz * mBtruez
         // mBmeasz - mBtruez - bz = sz * mBtruez
 
         // [mBtruex  0        0        mBtruey  mBtruez  0      ][sx ] = [mBmeasx - mBtruex - bx]
         // [0        mBtruey  0        0        0        mBtruez][sy ]   [mBmeasy - mBtruey - by]
         // [0        0        mBtruez  0        0        0      ][sz ]   [mBmeasz - mBtruez - bz]
         //                                                       [mxy]
         //                                                       [mxz]
         //                                                       [myz]
 
         fitter.setFunctionEvaluator(new LevenbergMarquardtMultiVariateFunctionEvaluator() {
             @Override
             public int getNumberOfDimensions() {
                 // Input points are true magnetic flux density coordinates
                 return BodyMagneticFluxDensity.COMPONENTS;
             }
 
             @Override
             public int getNumberOfVariables() {
                 // The multivariate function returns the components of measured magnetic flux density
                 return BodyMagneticFluxDensity.COMPONENTS;
             }
 
             @Override
             public double[] createInitialParametersArray() {
                 final var initial = new double[COMMON_Z_AXIS_UNKNOWNS];
 
                 initial[0] = initialSx;
                 initial[1] = initialSy;
                 initial[2] = initialSz;
 
                 initial[3] = initialMxy;
                 initial[4] = initialMxz;
                 initial[5] = initialMyz;
 
                 return initial;
             }
 
             @Override
             public void evaluate(
                     final int i, final double[] point, final double[] result, final double[] params,
                     final Matrix jacobian) {
                 // We know that:
                 // mBmeasx = bx + mBtruex + sx * mBtruex + mxy * mBtruey + mxz * mBtruez
                 // mBmeasy = by + mBtruey + sy * mBtruey + myz * mBtruez
                 // mBmeasz = bz + mBtruez + sz * mBtruez
 
                 // Hence, the derivatives respect the parameters sx, sy, sz,
                 // mxy, mxz, myz
 
                 // d(fmeasx)/d(sx) = mBtruex
                 // d(fmeasx)/d(sy) = 0.0
                 // d(fmeasx)/d(sz) = 0.0
                 // d(fmeasx)/d(mxy) = mBtruey
                 // d(fmeasx)/d(mxz) = mBtruez
                 // d(fmeasx)/d(myz) = 0.0
 
                 // d(fmeasy)/d(sx) = 0.0
                 // d(fmeasy)/d(sy) = mBtruey
                 // d(fmeasy)/d(sz) = 0.0
                 // d(fmeasy)/d(mxy) = 0.0
                 // d(fmeasy)/d(mxz) = 0.0
                 // d(fmeasy)/d(myz) = mBtruez
 
                 // d(fmeasz)/d(sx) = 0.0
                 // d(fmeasz)/d(sy) = 0.0
                 // d(fmeasz)/d(sz) = mBtruez
                 // d(fmeasz)/d(mxy) = 0.0
                 // d(fmeasz)/d(mxz) = 0.0
                 // d(fmeasz)/d(myz) = 0.0
 
                 final var sx = params[0];
                 final var sy = params[1];
                 final var sz = params[2];
 
                 final var mxy = params[3];
                 final var mxz = params[4];
                 final var myz = params[5];
 
                 final var btruex = point[0];
                 final var btruey = point[1];
                 final var btruez = point[2];
 
                 result[0] = hardIronX + btruex + sx * btruex + mxy * btruey + mxz * btruez;
                 result[1] = hardIronY + btruey + sy * btruey + myz * btruez;
                 result[2] = hardIronZ + btruez + sz * btruez;
 
                 jacobian.setElementAt(0, 0, btruex);
                 jacobian.setElementAt(0, 1, 0.0);
                 jacobian.setElementAt(0, 2, 0.0);
                 jacobian.setElementAt(0, 3, btruey);
                 jacobian.setElementAt(0, 4, btruez);
                 jacobian.setElementAt(0, 5, 0.0);
 
                 jacobian.setElementAt(1, 0, 0.0);
                 jacobian.setElementAt(1, 1, btruey);
                 jacobian.setElementAt(1, 2, 0.0);
                 jacobian.setElementAt(1, 3, 0.0);
                 jacobian.setElementAt(1, 4, 0.0);
                 jacobian.setElementAt(1, 5, btruez);
 
                 jacobian.setElementAt(2, 0, 0.0);
                 jacobian.setElementAt(2, 1, 0.0);
                 jacobian.setElementAt(2, 2, btruez);
                 jacobian.setElementAt(2, 3, 0.0);
                 jacobian.setElementAt(2, 4, 0.0);
                 jacobian.setElementAt(2, 5, 0.0);
             }
         });
 
         setInputData();
 
         fitter.fit();
 
         final var result = fitter.getA();
 
         final var sx = result[0];
         final var sy = result[1];
         final var sz = result[2];
 
         final var mxy = result[3];
         final var mxz = result[4];
         final var myz = result[5];
 
         if (estimatedMm == null) {
             estimatedMm = new Matrix(BodyMagneticFluxDensity.COMPONENTS, BodyMagneticFluxDensity.COMPONENTS);
         } else {
             estimatedMm.initialize(0.0);
         }
 
         estimatedMm.setElementAt(0, 0, sx);
 
         estimatedMm.setElementAt(0, 1, mxy);
         estimatedMm.setElementAt(1, 1, sy);
 
         estimatedMm.setElementAt(0, 2, mxz);
         estimatedMm.setElementAt(1, 2, myz);
         estimatedMm.setElementAt(2, 2, sz);
 
         estimatedCovariance = fitter.getCovar();
 
         // propagate covariance matrix so that all parameters are taken into
         // account in the order: sx, sy, sz, mxy, mxz, myx, myz, mzx, mzy
 
         // We define a lineal function mapping original parameters for the common
         // axis case to the general case
         // [sx'] = [1  0  0  0  0  0][sx]
         // [sy']   [0  1  0  0  0  0][sy]
         // [sz']   [0  0  1  0  0  0][sz]
         // [mxy']  [0  0  0  1  0  0][mxy]
         // [mxz']  [0  0  0  0  1  0][mxz]
         // [myx']  [0  0  0  0  0  0][myz]
         // [myz']  [0  0  0  0  0  1]
         // [mzx']  [0  0  0  0  0  0]
         // [mzy']  [0  0  0  0  0  0]
 
         // As defined in com.irurueta.statistics.MultivariateNormalDist,
         // if we consider the jacobian of the lineal application the matrix shown
         // above, then covariance can be propagated as follows
         final var jacobian = Matrix.identity(GENERAL_UNKNOWNS, COMMON_Z_AXIS_UNKNOWNS);
         jacobian.setElementAt(5, 5, 0.0);
         jacobian.setElementAt(6, 5, 1.0);
 
         // propagated covariance is J * Cov * J'
         final var jacobianTrans = jacobian.transposeAndReturnNew();
         jacobian.multiply(estimatedCovariance);
         jacobian.multiply(jacobianTrans);
         estimatedCovariance = jacobian;
         estimatedChiSq = fitter.getChisq();
         estimatedChiSqDegreesOfFreedom = fitter.getChisqDegreesOfFreedom();
         estimatedReducedChiSq = fitter.getReducedChisq();
         estimatedMse = fitter.getMse();
         try {
             estimatedP = fitter.getP();
             estimatedQ = fitter.getQ();
         } catch (final MaxIterationsExceededException ignore) {
             // if numerical instabilities arise, we assume worst case (no fit at all)
             // probability of finding a smaller chi square value is 1.0
             // quality of fit is 0.0
             estimatedP = 1.0;
             estimatedQ = 0.0;
         }
     }
 
     /**
      * Internal method to perform general calibration.
      *
      * @throws AlgebraException                         if there are numerical errors.
      * @throws FittingException                         if no convergence to solution is found.
      * @throws com.irurueta.numerical.NotReadyException if fitter is not ready.
      * @throws IOException                              if world magnetic model cannot be loaded.
      */
     private void calibrateGeneral() throws AlgebraException, FittingException,
             com.irurueta.numerical.NotReadyException, IOException {
         // The accelerometer model is:
         // mBmeas = ba + (I + Mm) * mBtrue + w
 
         // Ideally a least squares solution tries to minimize noise component, so:
         // mBmeas = ba + (I + Mm) * mBtrue
 
         // Hence:
         // [mBmeasx] = [bx] + ( [1  0   0] + [sx    mxy mxz])   [mBtruex]
         // [mBmeasy] = [by]     [0  1   0]   [myx   sy  myz]    [mBtruey]
         // [mBmeasz] = [bz]     [0  0   1]   [mzx   mzy sz ]    [mBtruez]
 
         // [mBmeasx] = [bx] +   [1+sx   mxy     mxz ][mBtruex]
         // [mBmeasy]   [by]     [myx    1+sy    myz ][mBtruey]
         // [mBmeasz]   [bz]     [mzx    mzy     1+sz][mBtruez]
 
         // mBmeasx = bx + (1+sx) * mBtruex + mxy * mBtruey + mxz * mBtruez
         // mBmeasy = by + myx * mBtruex + (1+sy) * mBtruey + myz * mBtruez
         // mBmeasz = bz + mzx * mBtruex + mzy * mBtruey + (1+sz) * mBtruez
 
         // Where the unknowns are: bx, by, bz, sx, sy, sz, mxy mxz, myx, myz, mzx, mzy
         // Reordering:
         // mBmeasx = bx + mBtruex + sx * mBtruex + mxy * mBtruey + mxz * mBtruez
         // mBmeasy = by + myx * mBtruex + mBtruey + sy * mBtruey + myz * mBtruez
         // mBmeasz = bz + mzx * mBtruex + mzy * mBtruey + mBtruez + sz * mBtruez
 
         // mBmeasx - mBtruex - bx = sx * mBtruex + mxy * mBtruey + mxz * mBtruez
         // mBmeasy - mBtruey - by = myx * mBtruex + sy * mBtruey + myz * mBtruez
         // mBmeasz - mBtruez - bz = mzx * mBtruex + mzy * mBtruey + sz * mBtruez
 
         // [mBtruex  0        0        mBtruey  mBtruez  0        0        0        0      ][sx ] = [mBmeasx - mBtruex - bx]
         // [0        mBtruey  0        0        0        mBtruex  mBtruez  0        0      ][sy ]   [mBmeasy - mBtruey - by]
         // [0        0        mBtruez  0        0        0        0        mBtruex  mBtruey][sz ]   [mBmeasz - mBtruez - bz]
         //                                                                                  [mxy]
         //                                                                                  [mxz]
         //                                                                                  [myx]
         //                                                                                  [myz]
         //                                                                                  [mzx]
         //                                                                                  [mzy]
 
         fitter.setFunctionEvaluator(new LevenbergMarquardtMultiVariateFunctionEvaluator() {
             @Override
             public int getNumberOfDimensions() {
                 // Input points are true magnetic flux density coordinates
                 return BodyMagneticFluxDensity.COMPONENTS;
             }
 
             @Override
             public int getNumberOfVariables() {
                 // The multivariate function returns the components of measured magnetic flux density
                 return BodyMagneticFluxDensity.COMPONENTS;
             }
 
             @Override
             public double[] createInitialParametersArray() {
                 final var initial = new double[GENERAL_UNKNOWNS];
 
                 initial[0] = initialSx;
                 initial[1] = initialSy;
                 initial[2] = initialSz;
 
                 initial[3] = initialMxy;
                 initial[4] = initialMxz;
                 initial[5] = initialMyx;
                 initial[6] = initialMyz;
                 initial[7] = initialMzx;
                 initial[8] = initialMzy;
 
                 return initial;
             }
 
             @Override
             public void evaluate(
                     final int i, final double[] point, final double[] result, final double[] params,
                     final Matrix jacobian) {
                 // We know that:
                 // mBmeasx = bx + mBtruex + sx * mBtruex + mxy * mBtruey + mxz * mBtruez
                 // mBmeasy = by + myx * mBtruex + mBtruey + sy * mBtruey + myz * mBtruez
                 // mBmeasz = bz + mzx * mBtruex + mzy * mBtruey + mBtruez + sz * mBtruez
 
                 // Hence, the derivatives respect the parameters sx, sy, sz,
                 // mxy, mxz, myx, myz, mzx and mzy is:
 
                 // d(fmeasx)/d(sx) = mBtruex
                 // d(fmeasx)/d(sy) = 0.0
                 // d(fmeasx)/d(sz) = 0.0
                 // d(fmeasx)/d(mxy) = mBtruey
                 // d(fmeasx)/d(mxz) = mBtruez
                 // d(fmeasx)/d(myx) = 0.0
                 // d(fmeasx)/d(myz) = 0.0
                 // d(fmeasx)/d(mzx) = 0.0
                 // d(fmeasx)/d(mzy) = 0.0
 
                 // d(fmeasy)/d(sx) = 0.0
                 // d(fmeasy)/d(sy) = mBtruey
                 // d(fmeasy)/d(sz) = 0.0
                 // d(fmeasy)/d(mxy) = 0.0
                 // d(fmeasy)/d(mxz) = 0.0
                 // d(fmeasy)/d(myx) = mBtruex
                 // d(fmeasy)/d(myz) = mBtruez
                 // d(fmeasy)/d(mzx) = 0.0
                 // d(fmeasy)/d(mzy) = 0.0
 
                 // d(fmeasz)/d(sx) = 0.0
                 // d(fmeasz)/d(sy) = 0.0
                 // d(fmeasz)/d(sz) = mBtruez
                 // d(fmeasz)/d(mxy) = 0.0
                 // d(fmeasz)/d(mxz) = 0.0
                 // d(fmeasz)/d(myx) = 0.0
                 // d(fmeasz)/d(myz) = 0.0
                 // d(fmeasz)/d(mzx) = mBtruex
                 // d(fmeasz)/d(mzy) = mBtruey
 
                 final var sx = params[0];
                 final var sy = params[1];
                 final var sz = params[2];
 
                 final var mxy = params[3];
                 final var mxz = params[4];
                 final var myx = params[5];
                 final var myz = params[6];
                 final var mzx = params[7];
                 final var mzy = params[8];
 
                 final var btruex = point[0];
                 final var btruey = point[1];
                 final var btruez = point[2];
 
                 result[0] = hardIronX + btruex + sx * btruex + mxy * btruey + mxz * btruez;
                 result[1] = hardIronY + myx * btruex + btruey + sy * btruey + myz * btruez;
                 result[2] = hardIronZ + mzx * btruex + mzy * btruey + btruez + sz * btruez;
 
                 jacobian.setElementAt(0, 0, btruex);
                 jacobian.setElementAt(0, 1, 0.0);
                 jacobian.setElementAt(0, 2, 0.0);
                 jacobian.setElementAt(0, 3, btruey);
                 jacobian.setElementAt(0, 4, btruez);
                 jacobian.setElementAt(0, 5, 0.0);
                 jacobian.setElementAt(0, 6, 0.0);
                 jacobian.setElementAt(0, 7, 0.0);
                 jacobian.setElementAt(0, 8, 0.0);
 
                 jacobian.setElementAt(1, 0, 0.0);
                 jacobian.setElementAt(1, 1, btruey);
                 jacobian.setElementAt(1, 2, 0.0);
                 jacobian.setElementAt(1, 3, 0.0);
                 jacobian.setElementAt(1, 4, 0.0);
                 jacobian.setElementAt(1, 5, btruex);
                 jacobian.setElementAt(1, 6, btruez);
                 jacobian.setElementAt(1, 7, 0.0);
                 jacobian.setElementAt(1, 8, 0.0);
 
                 jacobian.setElementAt(2, 0, 0.0);
                 jacobian.setElementAt(2, 1, 0.0);
                 jacobian.setElementAt(2, 2, btruez);
                 jacobian.setElementAt(2, 3, 0.0);
                 jacobian.setElementAt(2, 4, 0.0);
                 jacobian.setElementAt(2, 5, 0.0);
                 jacobian.setElementAt(2, 6, 0.0);
                 jacobian.setElementAt(2, 7, btruex);
                 jacobian.setElementAt(2, 8, btruey);
             }
         });
 
         setInputData();
 
         fitter.fit();
 
         final var result = fitter.getA();
 
         final var sx = result[0];
         final var sy = result[1];
         final var sz = result[2];
 
         final var mxy = result[3];
         final var mxz = result[4];
         final var myx = result[5];
         final var myz = result[6];
         final var mzx = result[7];
         final var mzy = result[8];
 
         if (estimatedMm == null) {
             estimatedMm = new Matrix(BodyMagneticFluxDensity.COMPONENTS, BodyMagneticFluxDensity.COMPONENTS);
         } else {
             estimatedMm.initialize(0.0);
         }
 
         estimatedMm.setElementAt(0, 0, sx);
         estimatedMm.setElementAt(1, 0, myx);
         estimatedMm.setElementAt(2, 0, mzx);
 
         estimatedMm.setElementAt(0, 1, mxy);
         estimatedMm.setElementAt(1, 1, sy);
         estimatedMm.setElementAt(2, 1, mzy);
 
         estimatedMm.setElementAt(0, 2, mxz);
         estimatedMm.setElementAt(1, 2, myz);
         estimatedMm.setElementAt(2, 2, sz);
 
         estimatedCovariance = fitter.getCovar();
         estimatedChiSq = fitter.getChisq();
         estimatedChiSqDegreesOfFreedom = fitter.getChisqDegreesOfFreedom();
         estimatedReducedChiSq = fitter.getReducedChisq();
         estimatedMse = fitter.getMse();
         try {
             estimatedP = fitter.getP();
             estimatedQ = fitter.getQ();
         } catch (final MaxIterationsExceededException ignore) {
             // if numerical instabilities arise, we assume worst case (no fit at all)
             // probability of finding a smaller chi square value is 1.0
             // quality of fit is 0.0
             estimatedP = 1.0;
             estimatedQ = 0.0;
         }
     }
 
     /**
      * Sets input data into Levenberg-Marquardt fitter.
      *
      * @throws WrongSizeException never happens.
      * @throws IOException        if world magnetic model cannot be loaded.
      */
     private void setInputData() throws WrongSizeException, IOException {
         // set input data using:
         // mBmeasx = bx + mBtruex + sx * mBtruex + mxy * mBtruey + mxz * mBtruez
         // mBmeasy = by + myx * mBtruex + mBtruey + sy * mBtruey + myz * mBtruez
         // mBmeasz = bz + mzx * mBtruex + mzy * mBtruey + mBtruez + sz * mBtruez
 
         final WMMEarthMagneticFluxDensityEstimator wmmEstimator;
         if (magneticModel != null) {
             wmmEstimator = new WMMEarthMagneticFluxDensityEstimator(magneticModel);
         } else {
             wmmEstimator = new WMMEarthMagneticFluxDensityEstimator();
         }
 
         final var expectedMagneticFluxDensity = new BodyMagneticFluxDensity();
         final var nedFrame = new NEDFrame();
         final var earthB = new NEDMagneticFluxDensity();
         final var cbn = new CoordinateTransformation(FrameType.BODY_FRAME, FrameType.LOCAL_NAVIGATION_FRAME);
         final var cnb = new CoordinateTransformation(FrameType.LOCAL_NAVIGATION_FRAME, FrameType.BODY_FRAME);
 
         final var numMeasurements = measurements.size();
         final var x = new Matrix(numMeasurements, BodyMagneticFluxDensity.COMPONENTS);
         final var y = new Matrix(numMeasurements, BodyMagneticFluxDensity.COMPONENTS);
         final var specificForceStandardDeviations = new double[numMeasurements];
         var i = 0;
         for (final var measurement : measurements) {
             final var measuredMagneticFluxDensity = measurement.getMagneticFluxDensity();
 
             // estimate Earth magnetic flux density at frame position and
             // timestamp using WMM
             final var ecefFrame = measurement.getFrame();
             ECEFtoNEDFrameConverter.convertECEFtoNED(ecefFrame, nedFrame);
 
             final var year = measurement.getYear();
 
             final var latitude = nedFrame.getLatitude();
             final var longitude = nedFrame.getLongitude();
             final var height = nedFrame.getHeight();
 
             nedFrame.getCoordinateTransformation(cbn);
             cbn.inverse(cnb);
 
             wmmEstimator.estimate(latitude, longitude, height, year, earthB);
 
             // estimate expected body magnetic flux density taking into
             // account body attitude (inverse of frame orientation) and
             // estimated Earth magnetic flux density
             BodyMagneticFluxDensityEstimator.estimate(earthB, cnb, expectedMagneticFluxDensity);
 
             final var bMeasX = measuredMagneticFluxDensity.getBx();
             final var bMeasY = measuredMagneticFluxDensity.getBy();
             final var bMeasZ = measuredMagneticFluxDensity.getBz();
 
             final var bTrueX = expectedMagneticFluxDensity.getBx();
             final var bTrueY = expectedMagneticFluxDensity.getBy();
             final var bTrueZ = expectedMagneticFluxDensity.getBz();
 
             x.setElementAt(i, 0, bTrueX);
             x.setElementAt(i, 1, bTrueY);
             x.setElementAt(i, 2, bTrueZ);
 
             y.setElementAt(i, 0, bMeasX);
             y.setElementAt(i, 1, bMeasY);
             y.setElementAt(i, 2, bMeasZ);
 
             specificForceStandardDeviations[i] = measurement.getMagneticFluxDensityStandardDeviation();
             i++;
         }
 
         fitter.setInputData(x, y, specificForceStandardDeviations);
     }
 
     /**
      * Converts magnetic flux density value and unit to Teslas.
      *
      * @param value magnetic flux density value.
      * @param unit  unit of magnetic flux density value.
      * @return converted value.
      */
     private static double convertMagneticFluxDensity(final double value, final MagneticFluxDensityUnit unit) {
         return MagneticFluxDensityConverter.convert(value, unit, MagneticFluxDensityUnit.TESLA);
     }
 
     /**
      * Converts magnetic flux density instance to Teslas.
      *
      * @param magneticFluxDensity magnetic flux density instance to be converted.
      * @return converted value.
      */
     private static double convertMagneticFluxDensity(final MagneticFluxDensity magneticFluxDensity) {
         return convertMagneticFluxDensity(magneticFluxDensity.getValue().doubleValue(), magneticFluxDensity.getUnit());
     }
 }