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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 a second order Runge-Kutta integrator for
22   * 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
28   *   1/2 | 1/2   0
29   *       |----------
30   *       |  0    1
31   * </pre>
32   * </p>
33   *
34   * @see EulerIntegrator
35   * @see ClassicalRungeKuttaIntegrator
36   * @see GillIntegrator
37   *
38   * @version $Revision: 620312 $ $Date: 2008-02-10 12:28:59 -0700 (Sun, 10 Feb 2008) $
39   * @since 1.2
40   */
41  
42  public class MidpointIntegrator
43    extends RungeKuttaIntegrator {
44  
45    /** Integrator method name. */
46    private static final String methodName = "midpoint";
47  
48    /** Time steps Butcher array. */
49    private static final double[] c = {
50      1.0 / 2.0
51    };
52  
53    /** Internal weights Butcher array. */
54    private static final double[][] a = {
55      { 1.0 / 2.0 }
56    };
57  
58    /** Propagation weights Butcher array. */
59    private static final double[] b = {
60      0.0, 1.0
61    };
62  
63    /** Simple constructor.
64     * Build a midpoint integrator with the given step.
65     * @param step integration step
66     */
67    public MidpointIntegrator(double step) {
68      super(c, a, b, new MidpointStepInterpolator(), step);
69    }
70  
71    /** Get the name of the method.
72     * @return name of the method
73     */
74    public String getName() {
75      return methodName;
76    }
77  
78  }