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
21 /**
22 * This class implements the classical fourth order Runge-Kutta
23 * integrator for Ordinary Differential Equations (it is the most
24 * often used Runge-Kutta method).
25 *
26 * <p>This method is an explicit Runge-Kutta method, its Butcher-array
27 * is the following one :
28 * <pre>
29 * 0 | 0 0 0 0
30 * 1/2 | 1/2 0 0 0
31 * 1/2 | 0 1/2 0 0
32 * 1 | 0 0 1 0
33 * |--------------------
34 * | 1/6 1/3 1/3 1/6
35 * </pre>
36 *
37 * @see EulerIntegrator
38 * @see GillIntegrator
39 * @see MidpointIntegrator
40 * @see ThreeEighthesIntegrator
41 * @see LutherIntegrator
42 * @since 1.2
43 */
44
45 public class ClassicalRungeKuttaIntegrator extends RungeKuttaIntegrator {
46
47 /** Time steps Butcher array. */
48 private static final double[] STATIC_C = {
49 1.0 / 2.0, 1.0 / 2.0, 1.0
50 };
51
52 /** Internal weights Butcher array. */
53 private static final double[][] STATIC_A = {
54 { 1.0 / 2.0 },
55 { 0.0, 1.0 / 2.0 },
56 { 0.0, 0.0, 1.0 }
57 };
58
59 /** Propagation weights Butcher array. */
60 private static final double[] STATIC_B = {
61 1.0 / 6.0, 1.0 / 3.0, 1.0 / 3.0, 1.0 / 6.0
62 };
63
64 /** Simple constructor.
65 * Build a fourth-order Runge-Kutta integrator with the given
66 * step.
67 * @param step integration step
68 */
69 public ClassicalRungeKuttaIntegrator(final double step) {
70 super("classical Runge-Kutta", STATIC_C, STATIC_A, STATIC_B,
71 new ClassicalRungeKuttaStepInterpolator(), step);
72 }
73 }