1 /*
2 * Copyright (C) 2023 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.numerical.integration;
17
18 import com.irurueta.numerical.EvaluationException;
19 import com.irurueta.numerical.SingleDimensionFunctionEvaluatorListener;
20
21 /**
22 * Implementation of quadrature using trapezoidal algorithm.
23 * This implementation is suitable for non-improper integrands, which consist
24 * of functions with not known singularities that can be evaluated on all the integration
25 * interval, which must be finite.
26 */
27 public class TrapezoidalQuadrature extends Quadrature {
28
29 /**
30 * Lower limit of integration.
31 */
32 private final double a;
33
34 /**
35 * Upper limit of integration.
36 */
37 private final double b;
38
39 /**
40 * Current value of integral.
41 */
42 private double s;
43
44 /**
45 * Listener to evaluate single dimension functions at required points.
46 */
47 private final SingleDimensionFunctionEvaluatorListener listener;
48
49 /**
50 * Constructor.
51 *
52 * @param a Lower limit of integration.
53 * @param b Upper limit of integration.
54 * @param listener listener to evaluate a single dimension function at required points.
55 */
56 public TrapezoidalQuadrature(
57 final double a, final double b, final SingleDimensionFunctionEvaluatorListener listener) {
58 this.n = 0;
59 this.a = a;
60 this.b = b;
61 this.s = 0;
62 this.listener = listener;
63 }
64
65 /**
66 * Gets lower limit of integration.
67 *
68 * @return lower limit of integration.
69 */
70 public double getA() {
71 return a;
72 }
73
74 /**
75 * Gets upper limit of integration.
76 *
77 * @return upper limit of integration.
78 */
79 public double getB() {
80 return b;
81 }
82
83 /**
84 * Gets current value of integral.
85 * @return current value of integral.
86 */
87 public double getS() {
88 return s;
89 }
90
91 /**
92 * Returns the value of the integral at the nth stage of refinement.
93 *
94 * @return the value of the integral at the nth stage of refinement.
95 * @throws EvaluationException Raised if something failed during the evaluation.
96 */
97 @Override
98 public double next() throws EvaluationException {
99 double x;
100 double tnm;
101 double sum;
102 double del;
103 int it;
104 int j;
105 n++;
106 if (n == 1) {
107 s = 0.5 * (b - a) * (listener.evaluate(a) + listener.evaluate(b));
108 return s;
109 } else {
110 for (it = 1, j = 1; j < n - 1; j++) {
111 it <<= 1;
112 }
113 tnm = it;
114 // This is the spacing of the points to be added
115 del = (b - a) / tnm;
116 x = a + 0.5 * del;
117 for (sum = 0.0, j = 0; j < it; j++, x += del) {
118 sum += listener.evaluate(x);
119 }
120 // This replaces s by its refined value
121 s = 0.5 * (s + (b - a) * sum / tnm);
122 return s;
123 }
124 }
125
126 /**
127 * Gets type of quadrature.
128 *
129 * @return type of quadrature.
130 */
131 @Override
132 public QuadratureType getType() {
133 return QuadratureType.TRAPEZOIDAL;
134 }
135 }