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 /** Simple constructor.
47 * Build a midpoint integrator with the given step.
48 * @param step integration step
49 */
50 public MidpointIntegrator(final double step) {
51 super("midpoint", step);
52 }
53
54 /** {@inheritDoc} */
55 @Override
56 public double[] getC() {
57 return new double[] {
58 1.0 / 2.0
59 };
60 }
61
62 /** {@inheritDoc} */
63 @Override
64 public double[][] getA() {
65 return new double[][] {
66 { 1.0 / 2.0 }
67 };
68 }
69
70 /** {@inheritDoc} */
71 @Override
72 public double[] getB() {
73 return new double[] {
74 0.0, 1.0
75 };
76 }
77
78 /** {@inheritDoc} */
79 @Override
80 protected MidpointStateInterpolator
81 createInterpolator(final boolean forward, double[][] yDotK,
82 final ODEStateAndDerivative globalPreviousState,
83 final ODEStateAndDerivative globalCurrentState,
84 final EquationsMapper mapper) {
85 return new MidpointStateInterpolator(forward, yDotK,
86 globalPreviousState, globalCurrentState,
87 globalPreviousState, globalCurrentState,
88 mapper);
89 }
90
91 }