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