1 /*
2 * Licensed to the Hipparchus project 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 Hipparchus project 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 * https://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.hipparchus.ode.nonstiff;
19
20 import org.hipparchus.ode.EquationsMapper;
21 import org.hipparchus.ode.ODEStateAndDerivative;
22
23 /**
24 * This class implements a second order Runge-Kutta integrator for
25 * Ordinary Differential Equations.
26 *
27 * <p>This method is an explicit Runge-Kutta method, its Butcher-array
28 * is the following one :</p>
29 * <pre>
30 * 0 | 0 0
31 * 1/2 | 1/2 0
32 * |----------
33 * | 0 1
34 * </pre>
35 *
36 * @see EulerIntegrator
37 * @see ClassicalRungeKuttaIntegrator
38 * @see GillIntegrator
39 * @see ThreeEighthesIntegrator
40 * @see LutherIntegrator
41 *
42 */
43
44 public class MidpointIntegrator extends RungeKuttaIntegrator {
45
46 /** Name of integration scheme. */
47 public static final String METHOD_NAME = "midpoint";
48
49 /** Simple constructor.
50 * Build a midpoint integrator with the given step.
51 * @param step integration step
52 */
53 public MidpointIntegrator(final double step) {
54 super(METHOD_NAME, step);
55 }
56
57 /** {@inheritDoc} */
58 @Override
59 public double[] getC() {
60 return new double[] {
61 1.0 / 2.0
62 };
63 }
64
65 /** {@inheritDoc} */
66 @Override
67 public double[][] getA() {
68 return new double[][] {
69 { 1.0 / 2.0 }
70 };
71 }
72
73 /** {@inheritDoc} */
74 @Override
75 public double[] getB() {
76 return new double[] {
77 0.0, 1.0
78 };
79 }
80
81 /** {@inheritDoc} */
82 @Override
83 protected MidpointStateInterpolator
84 createInterpolator(final boolean forward, double[][] yDotK,
85 final ODEStateAndDerivative globalPreviousState,
86 final ODEStateAndDerivative globalCurrentState,
87 final EquationsMapper mapper) {
88 return new MidpointStateInterpolator(forward, yDotK,
89 globalPreviousState, globalCurrentState,
90 globalPreviousState, globalCurrentState,
91 mapper);
92 }
93
94 }