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 * https://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 /*
19 * This is not the original file distributed by the Apache Software Foundation
20 * It has been modified by the Hipparchus project
21 */
22
23 package org.hipparchus.ode.nonstiff;
24
25 import org.hipparchus.CalculusFieldElement;
26 import org.hipparchus.Field;
27 import org.hipparchus.ode.FieldEquationsMapper;
28 import org.hipparchus.ode.FieldODEStateAndDerivative;
29 import org.hipparchus.util.MathArrays;
30
31 /**
32 * This class implements the 3/8 fourth order Runge-Kutta
33 * integrator for Ordinary Differential Equations.
34 *
35 * <p>This method is an explicit Runge-Kutta method, its Butcher-array
36 * is the following one :</p>
37 * <pre>
38 * 0 | 0 0 0 0
39 * 1/3 | 1/3 0 0 0
40 * 2/3 |-1/3 1 0 0
41 * 1 | 1 -1 1 0
42 * |--------------------
43 * | 1/8 3/8 3/8 1/8
44 * </pre>
45 *
46 * @see EulerFieldIntegrator
47 * @see ClassicalRungeKuttaFieldIntegrator
48 * @see GillFieldIntegrator
49 * @see MidpointFieldIntegrator
50 * @see LutherFieldIntegrator
51 * @param <T> the type of the field elements
52 */
53
54 public class ThreeEighthesFieldIntegrator<T extends CalculusFieldElement<T>>
55 extends RungeKuttaFieldIntegrator<T> {
56
57 /** Name of integration scheme. */
58 public static final String METHOD_NAME = ThreeEighthesIntegrator.METHOD_NAME;
59
60 /** Simple constructor.
61 * Build a 3/8 integrator with the given step.
62 * @param field field to which the time and state vector elements belong
63 * @param step integration step
64 */
65 public ThreeEighthesFieldIntegrator(final Field<T> field, final T step) {
66 super(field, METHOD_NAME, step);
67 }
68
69 /** {@inheritDoc} */
70 @Override
71 public T[] getC() {
72 final T[] c = MathArrays.buildArray(getField(), 3);
73 c[0] = FieldExplicitRungeKuttaIntegrator.fraction(getField(), 1, 3);
74 c[1] = c[0].add(c[0]);
75 c[2] = getField().getOne();
76 return c;
77 }
78
79 /** {@inheritDoc} */
80 @Override
81 public T[][] getA() {
82 final T[][] a = MathArrays.buildArray(getField(), 3, -1);
83 for (int i = 0; i < a.length; ++i) {
84 a[i] = MathArrays.buildArray(getField(), i + 1);
85 }
86 a[0][0] = FieldExplicitRungeKuttaIntegrator.fraction(getField(), 1, 3);
87 a[1][0] = a[0][0].negate();
88 a[1][1] = getField().getOne();
89 a[2][0] = getField().getOne();
90 a[2][1] = getField().getOne().negate();
91 a[2][2] = getField().getOne();
92 return a;
93 }
94
95 /** {@inheritDoc} */
96 @Override
97 public T[] getB() {
98 final T[] b = MathArrays.buildArray(getField(), 4);
99 b[0] = FieldExplicitRungeKuttaIntegrator.fraction(getField(), 1, 8);
100 b[1] = FieldExplicitRungeKuttaIntegrator.fraction(getField(), 3, 8);
101 b[2] = b[1];
102 b[3] = b[0];
103 return b;
104 }
105
106 /** {@inheritDoc} */
107 @Override
108 protected ThreeEighthesFieldStateInterpolator<T>
109 createInterpolator(final boolean forward, T[][] yDotK,
110 final FieldODEStateAndDerivative<T> globalPreviousState,
111 final FieldODEStateAndDerivative<T> globalCurrentState,
112 final FieldEquationsMapper<T> mapper) {
113 return new ThreeEighthesFieldStateInterpolator<T>(getField(), forward, yDotK,
114 globalPreviousState, globalCurrentState,
115 globalPreviousState, globalCurrentState,
116 mapper);
117 }
118
119 }