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.math.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 * </p>
36 *
37 * @see EulerIntegrator
38 * @see ClassicalRungeKuttaIntegrator
39 * @see GillIntegrator
40 * @see MidpointIntegrator
41 * @version $Revision: 786881 $ $Date: 2009-06-20 14:53:08 -0400 (Sat, 20 Jun 2009) $
42 * @since 1.2
43 */
44
45 public class ThreeEighthesIntegrator extends RungeKuttaIntegrator {
46
47 /** Time steps Butcher array. */
48 private static final double[] c = {
49 1.0 / 3.0, 2.0 / 3.0, 1.0
50 };
51
52 /** Internal weights Butcher array. */
53 private static final double[][] a = {
54 { 1.0 / 3.0 },
55 { -1.0 / 3.0, 1.0 },
56 { 1.0, -1.0, 1.0 }
57 };
58
59 /** Propagation weights Butcher array. */
60 private static final double[] b = {
61 1.0 / 8.0, 3.0 / 8.0, 3.0 / 8.0, 1.0 / 8.0
62 };
63
64 /** Simple constructor.
65 * Build a 3/8 integrator with the given step.
66 * @param step integration step
67 */
68 public ThreeEighthesIntegrator(final double step) {
69 super("3/8", c, a, b, new ThreeEighthesStepInterpolator(), step);
70 }
71
72 }