1 /*
2 * Licensed to the Hipparchus project 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 Hipparchus project 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 package org.hipparchus.ode.nonstiff;
19
20 import org.hipparchus.ode.EquationsMapper;
21 import org.hipparchus.ode.ODEStateAndDerivative;
22
23 /**
24 * This class implements the classical fourth order Runge-Kutta
25 * integrator for Ordinary Differential Equations (it is the most
26 * often used Runge-Kutta method).
27 *
28 * <p>This method is an explicit Runge-Kutta method, its Butcher-array
29 * is the following one :</p>
30 * <pre>
31 * 0 | 0 0 0 0
32 * 1/2 | 1/2 0 0 0
33 * 1/2 | 0 1/2 0 0
34 * 1 | 0 0 1 0
35 * |--------------------
36 * | 1/6 1/3 1/3 1/6
37 * </pre>
38 *
39 * @see EulerIntegrator
40 * @see GillIntegrator
41 * @see MidpointIntegrator
42 * @see ThreeEighthesIntegrator
43 * @see LutherIntegrator
44 */
45
46 public class ClassicalRungeKuttaIntegrator extends RungeKuttaIntegrator {
47
48 /** Name of integration scheme. */
49 public static final String METHOD_NAME = "classical Runge-Kutta";
50
51 /** Simple constructor.
52 * Build a fourth-order Runge-Kutta integrator with the given
53 * step.
54 * @param step integration step
55 */
56 public ClassicalRungeKuttaIntegrator(final double step) {
57 super(METHOD_NAME, step);
58 }
59
60 /** {@inheritDoc} */
61 @Override
62 public double[] getC() {
63 return new double[] {
64 1.0 / 2.0, 1.0 / 2.0, 1.0
65 };
66 }
67
68 /** {@inheritDoc} */
69 @Override
70 public double[][] getA() {
71 return new double[][] {
72 { 1.0 / 2.0 },
73 { 0.0, 1.0 / 2.0 },
74 { 0.0, 0.0, 1.0 }
75 };
76 }
77
78 /** {@inheritDoc} */
79 @Override
80 public double[] getB() {
81 return new double[] {
82 1.0 / 6.0, 1.0 / 3.0, 1.0 / 3.0, 1.0 / 6.0
83 };
84 }
85
86 /** {@inheritDoc} */
87 @Override
88 protected ClassicalRungeKuttaStateInterpolator
89 createInterpolator(final boolean forward, double[][] yDotK,
90 final ODEStateAndDerivative globalPreviousState,
91 final ODEStateAndDerivative globalCurrentState,
92 final EquationsMapper mapper) {
93 return new ClassicalRungeKuttaStateInterpolator(forward, yDotK,
94 globalPreviousState, globalCurrentState,
95 globalPreviousState, globalCurrentState,
96 mapper);
97 }
98
99 }