ExponentialMidPointMatrixQuadrature.java

/*
 * Copyright (C) 2023 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.numerical.integration;

import com.irurueta.algebra.Matrix;
import com.irurueta.algebra.WrongSizeException;
import com.irurueta.numerical.EvaluationException;

/**
 * This is an exact replacement for MidPointMatrixQuadrature, except that upper limit is assumed to be
 * infinite. It is assumed that the function decreases exponentially rapidly at infinity.
 */
public class ExponentialMidPointMatrixQuadrature extends MidPointMatrixQuadrature {

   /**
    * Constructor.
    *
    * @param a        Lower limit of integration.
    * @param listener listener to evaluate a single dimension function at required points.
    * @throws WrongSizeException if size notified by provided listener is invalid.
    */
   public ExponentialMidPointMatrixQuadrature(
           final double a, final MatrixSingleDimensionFunctionEvaluatorListener listener) throws WrongSizeException {
      super(0.0, Math.exp(-a), listener);
   }

   /**
    * Gets type of quadrature.
    *
    * @return type of quadrature.
    */
   @Override
   public QuadratureType getType() {
      return QuadratureType.EXPONENTIAL_MID_POINT;
   }

   /**
    * Evaluates function at f(-log(x))/x.
    *
    * @param x point where function is evaluated.
    * @param result instance where result of evaluation is stored.
    * @throws EvaluationException if evaluation fails.
    */
   @Override
   protected void func(final double x, final Matrix result) throws EvaluationException {
      listener.evaluate(-Math.log(x), result);
      result.multiplyByScalar(1.0 / x);
   }
}