1 /*
2 * Copyright (C) 2012 Alberto Irurueta Carro (alberto@irurueta.com)
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16 package com.irurueta.algebra;
17
18 /**
19 * Class in charge of computing Frobenius norms of vectors and matrices.
20 */
21 public class FrobeniusNormComputer extends NormComputer {
22
23 /**
24 * Constructor of this class.
25 */
26 public FrobeniusNormComputer() {
27 super();
28 }
29
30 /**
31 * Returns norm type being used by this class.
32 *
33 * @return Norm type being used by this class.
34 */
35 @Override
36 public NormType getNormType() {
37 return NormType.FROBENIUS_NORM;
38 }
39
40 /**
41 * Computes norm of provided matrix.
42 *
43 * @param m matrix being used for norm computation.
44 * @return norm of provided matrix.
45 */
46 public static double norm(final Matrix m) {
47 final var rows = m.getRows();
48 final var columns = m.getColumns();
49 final var length = rows * columns;
50 var sum = 0.0;
51 double value;
52 for (var i = 0; i < length; i++) {
53 value = m.getElementAtIndex(i);
54 sum += value * value;
55 }
56 return Math.sqrt(sum);
57 }
58
59 /**
60 * Computes norm of provided array and stores the jacobian into provided
61 * instance.
62 *
63 * @param array array being used for norm computation.
64 * @param jacobian instance where jacobian will be stored. Must be 1xN,
65 * where N is length of array.
66 * @return norm of provided vector.
67 * @throws WrongSizeException if provided jacobian is not 1xN, where N is
68 * length of array.
69 */
70 public static double norm(final double[] array, final Matrix jacobian) throws WrongSizeException {
71 if (jacobian != null && (jacobian.getRows() != 1 || jacobian.getColumns() != array.length)) {
72 throw new WrongSizeException();
73 }
74
75 final var norm = FrobeniusNormComputer.norm(array);
76
77 if (jacobian != null) {
78 jacobian.fromArray(array);
79 jacobian.multiplyByScalar(1.0 / norm);
80 }
81
82 return norm;
83 }
84
85 /**
86 * Computes norm of provided matrix.
87 *
88 * @param m Matrix being used for norm computation.
89 * @return Norm of provided matrix.
90 */
91 @Override
92 public double getNorm(final Matrix m) {
93 return norm(m);
94 }
95
96 /**
97 * Computes norm of provided array.
98 *
99 * @param array array being used for norm computation.
100 * @return norm of provided vector.
101 */
102 public static double norm(final double[] array) {
103 var sum = 0.0;
104 for (final var value : array) {
105 sum += value * value;
106 }
107 return Math.sqrt(sum);
108 }
109
110 /**
111 * Computes norm of provided array.
112 *
113 * @param array Array being used for norm computation.
114 * @return Norm of provided vector.
115 */
116 @Override
117 public double getNorm(final double[] array) {
118 return norm(array);
119 }
120 }