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 3/8 fourth order Runge-Kutta
23 * integrator for Ordinary Differential Equations.
24 *
25 * <p>This method is an explicit Runge-Kutta method, its Butcher-array
26 * is the following one :
27 * <pre>
28 * 0 | 0 0 0 0
29 * 1/3 | 1/3 0 0 0
30 * 2/3 |-1/3 1 0 0
31 * 1 | 1 -1 1 0
32 * |--------------------
33 * | 1/8 3/8 3/8 1/8
34 * </pre>
35 *
36 * @see EulerIntegrator
37 * @see ClassicalRungeKuttaIntegrator
38 * @see GillIntegrator
39 * @see MidpointIntegrator
40 * @see LutherIntegrator
41 * @since 1.2
42 */
43
44 public class ThreeEighthesIntegrator extends RungeKuttaIntegrator {
45
46 /** Time steps Butcher array. */
47 private static final double[] STATIC_C = {
48 1.0 / 3.0, 2.0 / 3.0, 1.0
49 };
50
51 /** Internal weights Butcher array. */
52 private static final double[][] STATIC_A = {
53 { 1.0 / 3.0 },
54 { -1.0 / 3.0, 1.0 },
55 { 1.0, -1.0, 1.0 }
56 };
57
58 /** Propagation weights Butcher array. */
59 private static final double[] STATIC_B = {
60 1.0 / 8.0, 3.0 / 8.0, 3.0 / 8.0, 1.0 / 8.0
61 };
62
63 /** Simple constructor.
64 * Build a 3/8 integrator with the given step.
65 * @param step integration step
66 */
67 public ThreeEighthesIntegrator(final double step) {
68 super("3/8", STATIC_C, STATIC_A, STATIC_B, new ThreeEighthesStepInterpolator(), step);
69 }
70 }