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 a second order Runge-Kutta integrator for
23 * 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
29 * 1/2 | 1/2 0
30 * |----------
31 * | 0 1
32 * </pre>
33 *
34 * @see EulerIntegrator
35 * @see ClassicalRungeKuttaIntegrator
36 * @see GillIntegrator
37 * @see ThreeEighthesIntegrator
38 * @see LutherIntegrator
39 *
40 * @since 1.2
41 */
42
43 public class MidpointIntegrator extends RungeKuttaIntegrator {
44
45 /** Time steps Butcher array. */
46 private static final double[] STATIC_C = {
47 1.0 / 2.0
48 };
49
50 /** Internal weights Butcher array. */
51 private static final double[][] STATIC_A = {
52 { 1.0 / 2.0 }
53 };
54
55 /** Propagation weights Butcher array. */
56 private static final double[] STATIC_B = {
57 0.0, 1.0
58 };
59
60 /** Simple constructor.
61 * Build a midpoint integrator with the given step.
62 * @param step integration step
63 */
64 public MidpointIntegrator(final double step) {
65 super("midpoint", STATIC_C, STATIC_A, STATIC_B, new MidpointStepInterpolator(), step);
66 }
67 }