1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18 package org.apache.commons.math4.legacy.ode.nonstiff;
19
20 import org.apache.commons.math4.legacy.core.Field;
21 import org.apache.commons.math4.legacy.core.RealFieldElement;
22 import org.apache.commons.math4.legacy.ode.FieldEquationsMapper;
23 import org.apache.commons.math4.legacy.ode.FieldODEStateAndDerivative;
24 import org.apache.commons.math4.legacy.core.MathArrays;
25
26 /**
27 * This class implements the classical fourth order Runge-Kutta
28 * integrator for Ordinary Differential Equations (it is the most
29 * often used Runge-Kutta method).
30 *
31 * <p>This method is an explicit Runge-Kutta method, its Butcher-array
32 * is the following one :
33 * <pre>
34 * 0 | 0 0 0 0
35 * 1/2 | 1/2 0 0 0
36 * 1/2 | 0 1/2 0 0
37 * 1 | 0 0 1 0
38 * |--------------------
39 * | 1/6 1/3 1/3 1/6
40 * </pre>
41 *
42 * @see EulerFieldIntegrator
43 * @see GillFieldIntegrator
44 * @see MidpointFieldIntegrator
45 * @see ThreeEighthesFieldIntegrator
46 * @see LutherFieldIntegrator
47 * @param <T> the type of the field elements
48 * @since 3.6
49 */
50
51 public class ClassicalRungeKuttaFieldIntegrator<T extends RealFieldElement<T>>
52 extends RungeKuttaFieldIntegrator<T> {
53
54 /** Simple constructor.
55 * Build a fourth-order Runge-Kutta integrator with the given step.
56 * @param field field to which the time and state vector elements belong
57 * @param step integration step
58 */
59 public ClassicalRungeKuttaFieldIntegrator(final Field<T> field, final T step) {
60 super(field, "classical Runge-Kutta", step);
61 }
62
63 /** {@inheritDoc} */
64 @Override
65 public T[] getC() {
66 final T[] c = MathArrays.buildArray(getField(), 3);
67 c[0] = getField().getOne().multiply(0.5);
68 c[1] = c[0];
69 c[2] = getField().getOne();
70 return c;
71 }
72
73 /** {@inheritDoc} */
74 @Override
75 public T[][] getA() {
76 final T[][] a = MathArrays.buildArray(getField(), 3, -1);
77 for (int i = 0; i < a.length; ++i) {
78 a[i] = MathArrays.buildArray(getField(), i + 1);
79 }
80 a[0][0] = fraction(1, 2);
81 a[1][0] = getField().getZero();
82 a[1][1] = a[0][0];
83 a[2][0] = getField().getZero();
84 a[2][1] = getField().getZero();
85 a[2][2] = getField().getOne();
86 return a;
87 }
88
89 /** {@inheritDoc} */
90 @Override
91 public T[] getB() {
92 final T[] b = MathArrays.buildArray(getField(), 4);
93 b[0] = fraction(1, 6);
94 b[1] = fraction(1, 3);
95 b[2] = b[1];
96 b[3] = b[0];
97 return b;
98 }
99
100 /** {@inheritDoc} */
101 @Override
102 protected ClassicalRungeKuttaFieldStepInterpolator<T>
103 createInterpolator(final boolean forward, T[][] yDotK,
104 final FieldODEStateAndDerivative<T> globalPreviousState,
105 final FieldODEStateAndDerivative<T> globalCurrentState,
106 final FieldEquationsMapper<T> mapper) {
107 return new ClassicalRungeKuttaFieldStepInterpolator<>(getField(), forward, yDotK,
108 globalPreviousState, globalCurrentState,
109 globalPreviousState, globalCurrentState,
110 mapper);
111 }
112 }