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.ThreeEighthesStateInterpolator;
23
24 /**
25 * This class implements the 3/8 fourth order Runge-Kutta
26 * integrator for 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 0 0
32 * 1/3 | 1/3 0 0 0
33 * 2/3 |-1/3 1 0 0
34 * 1 | 1 -1 1 0
35 * |--------------------
36 * | 1/8 3/8 3/8 1/8
37 * </pre>
38 *
39 * @see EulerIntegrator
40 * @see ClassicalRungeKuttaIntegrator
41 * @see GillIntegrator
42 * @see MidpointIntegrator
43 * @see LutherIntegrator
44 */
45
46 public class ThreeEighthesIntegrator extends FixedStepRungeKuttaIntegrator {
47
48 /** Name of integration scheme. */
49 public static final String METHOD_NAME = "3/8";
50
51 /** Simple constructor.
52 * Build a 3/8 integrator with the given step.
53 * @param step integration step
54 */
55 public ThreeEighthesIntegrator(final double step) {
56 super(METHOD_NAME, step);
57 }
58
59 /** {@inheritDoc} */
60 @Override
61 public double[] getC() {
62 return new double[] {
63 1.0 / 3.0, 2.0 / 3.0, 1.0
64 };
65 }
66
67 /** {@inheritDoc} */
68 @Override
69 public double[][] getA() {
70 return new double[][] {
71 { 1.0 / 3.0 },
72 { -1.0 / 3.0, 1.0 },
73 { 1.0, -1.0, 1.0 }
74 };
75 }
76
77 /** {@inheritDoc} */
78 @Override
79 public double[] getB() {
80 return new double[] {
81 1.0 / 8.0, 3.0 / 8.0, 3.0 / 8.0, 1.0 / 8.0
82 };
83 }
84
85 /** {@inheritDoc} */
86 @Override
87 protected ThreeEighthesStateInterpolator createInterpolator(final boolean forward, final double[][] yDotK,
88 final ODEStateAndDerivative globalPreviousState,
89 final ODEStateAndDerivative globalCurrentState,
90 final EquationsMapper mapper) {
91 return new ThreeEighthesStateInterpolator(forward, yDotK, globalPreviousState, globalCurrentState,
92 globalPreviousState, globalCurrentState, mapper);
93 }
94
95 }