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;
19
20 /**
21 * This class implements the 3/8 fourth order Runge-Kutta
22 * integrator for Ordinary Differential Equations.
23 *
24 * <p>This method is an explicit Runge-Kutta method, its Butcher-array
25 * is the following one :
26 * <pre>
27 * 0 | 0 0 0 0
28 * 1/3 | 1/3 0 0 0
29 * 2/3 |-1/3 1 0 0
30 * 1 | 1 -1 1 0
31 * |--------------------
32 * | 1/8 3/8 3/8 1/8
33 * </pre>
34 * </p>
35 *
36 * @see EulerIntegrator
37 * @see ClassicalRungeKuttaIntegrator
38 * @see GillIntegrator
39 * @see MidpointIntegrator
40 * @version $Revision: 620312 $ $Date: 2008-02-10 12:28:59 -0700 (Sun, 10 Feb 2008) $
41 * @since 1.2
42 */
43
44 public class ThreeEighthesIntegrator
45 extends RungeKuttaIntegrator {
46
47 /** Integrator method name. */
48 private static final String methodName = "3/8";
49
50 /** Time steps Butcher array. */
51 private static final double[] c = {
52 1.0 / 3.0, 2.0 / 3.0, 1.0
53 };
54
55 /** Internal weights Butcher array. */
56 private static final double[][] a = {
57 { 1.0 / 3.0 },
58 { -1.0 / 3.0, 1.0 },
59 { 1.0, -1.0, 1.0 }
60 };
61
62 /** Propagation weights Butcher array. */
63 private static final double[] b = {
64 1.0 / 8.0, 3.0 / 8.0, 3.0 / 8.0, 1.0 / 8.0
65 };
66
67 /** Simple constructor.
68 * Build a 3/8 integrator with the given step.
69 * @param step integration step
70 */
71 public ThreeEighthesIntegrator(double step) {
72 super(c, a, b, new ThreeEighthesStepInterpolator(), step);
73 }
74
75 /** Get the name of the method.
76 * @return name of the method
77 */
78 public String getName() {
79 return methodName;
80 }
81
82 }