View Javadoc

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 classical fourth order Runge-Kutta
22   * integrator for Ordinary Differential Equations (it is the most
23   * often used Runge-Kutta method).
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   *   1/2 | 1/2   0    0    0
30   *   1/2 |  0   1/2   0    0
31   *    1  |  0    0    1    0
32   *       |--------------------
33   *       | 1/6  1/3  1/3  1/6
34   * </pre>
35   * </p>
36   *
37   * @see EulerIntegrator
38   * @see GillIntegrator
39   * @see MidpointIntegrator
40   * @see ThreeEighthesIntegrator
41   * @version $Revision: 620312 $ $Date: 2008-02-10 12:28:59 -0700 (Sun, 10 Feb 2008) $
42   * @since 1.2
43   */
44  
45  public class ClassicalRungeKuttaIntegrator
46    extends RungeKuttaIntegrator {
47  
48    /** Integrator method name. */
49    private static final String methodName = "classical Runge-Kutta";
50  
51    /** Time steps Butcher array. */
52    private static final double[] c = {
53      1.0 / 2.0, 1.0 / 2.0, 1.0
54    };
55  
56    /** Internal weights Butcher array. */
57    private static final double[][] a = {
58      { 1.0 / 2.0 },
59      { 0.0, 1.0 / 2.0 },
60      { 0.0, 0.0, 1.0 }
61    };
62  
63    /** Propagation weights Butcher array. */
64    private static final double[] b = {
65      1.0 / 6.0, 1.0 / 3.0, 1.0 / 3.0, 1.0 / 6.0
66    };
67  
68    /** Simple constructor.
69     * Build a fourth-order Runge-Kutta integrator with the given
70     * step.
71     * @param step integration step
72     */
73    public ClassicalRungeKuttaIntegrator(double step) {
74      super(c, a, b, new ClassicalRungeKuttaStepInterpolator(), step);
75    }
76  
77    /** Get the name of the method.
78     * @return name of the method
79     */
80    public String getName() {
81      return methodName;
82    }
83  
84  }