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 the 3/8 fourth order Runge-Kutta
25 * integrator for 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 0 0
31 * 1/3 | 1/3 0 0 0
32 * 2/3 |-1/3 1 0 0
33 * 1 | 1 -1 1 0
34 * |--------------------
35 * | 1/8 3/8 3/8 1/8
36 * </pre>
37 *
38 * @see EulerIntegrator
39 * @see ClassicalRungeKuttaIntegrator
40 * @see GillIntegrator
41 * @see MidpointIntegrator
42 * @see LutherIntegrator
43 */
44
45 public class ThreeEighthesIntegrator extends RungeKuttaIntegrator {
46
47 /** Name of integration scheme. */
48 public static final String METHOD_NAME = "3/8";
49
50 /** Simple constructor.
51 * Build a 3/8 integrator with the given step.
52 * @param step integration step
53 */
54 public ThreeEighthesIntegrator(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 / 3.0, 2.0 / 3.0, 1.0
63 };
64 }
65
66 /** {@inheritDoc} */
67 @Override
68 public double[][] getA() {
69 return new double[][] {
70 { 1.0 / 3.0 },
71 { -1.0 / 3.0, 1.0 },
72 { 1.0, -1.0, 1.0 }
73 };
74 }
75
76 /** {@inheritDoc} */
77 @Override
78 public double[] getB() {
79 return new double[] {
80 1.0 / 8.0, 3.0 / 8.0, 3.0 / 8.0, 1.0 / 8.0
81 };
82 }
83
84 /** {@inheritDoc} */
85 @Override
86 protected ThreeEighthesStateInterpolator
87 createInterpolator(final boolean forward, double[][] yDotK,
88 final ODEStateAndDerivative globalPreviousState,
89 final ODEStateAndDerivative globalCurrentState,
90 final EquationsMapper mapper) {
91 return new ThreeEighthesStateInterpolator(forward, yDotK,
92 globalPreviousState, globalCurrentState,
93 globalPreviousState, globalCurrentState,
94 mapper);
95 }
96
97 }