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.GillStateInterpolator;
23 import org.hipparchus.util.FastMath;
24
25
26 /**
27 * This class implements the Gill fourth order Runge-Kutta
28 * integrator for Ordinary Differential Equations .
29
30 * <p>This method is an explicit Runge-Kutta method, its Butcher-array
31 * is the following one :</p>
32 * <pre>
33 * 0 | 0 0 0 0
34 * 1/2 | 1/2 0 0 0
35 * 1/2 | (q-1)/2 (2-q)/2 0 0
36 * 1 | 0 -q/2 (2+q)/2 0
37 * |-------------------------------
38 * | 1/6 (2-q)/6 (2+q)/6 1/6
39 * </pre>
40 * <p>where q = sqrt(2)</p>
41 *
42 * @see EulerIntegrator
43 * @see ClassicalRungeKuttaIntegrator
44 * @see MidpointIntegrator
45 * @see ThreeEighthesIntegrator
46 * @see LutherIntegrator
47 */
48
49 public class GillIntegrator extends FixedStepRungeKuttaIntegrator {
50
51 /** Name of integration scheme. */
52 public static final String METHOD_NAME = "Gill";
53
54 /** Simple constructor.
55 * Build a fourth-order Gill integrator with the given step.
56 * @param step integration step
57 */
58 public GillIntegrator(final double step) {
59 super(METHOD_NAME, step);
60 }
61
62 /** {@inheritDoc} */
63 @Override
64 public double[] getC() {
65 return new double[] {
66 1.0 / 2.0, 1.0 / 2.0, 1.0
67 };
68 }
69
70 /** {@inheritDoc} */
71 @Override
72 public double[][] getA() {
73 return new double[][] {
74 { 1.0 / 2.0 },
75 { (FastMath.sqrt(2.0) - 1.0) / 2.0, (2.0 - FastMath.sqrt(2.0)) / 2.0 },
76 { 0.0, -FastMath.sqrt(2.0) / 2.0, (2.0 + FastMath.sqrt(2.0)) / 2.0 }
77 };
78 }
79
80 /** {@inheritDoc} */
81 @Override
82 public double[] getB() {
83 return new double[] {
84 1.0 / 6.0, (2.0 - FastMath.sqrt(2.0)) / 6.0, (2.0 + FastMath.sqrt(2.0)) / 6.0, 1.0 / 6.0
85 };
86 }
87
88 /** {@inheritDoc} */
89 @Override
90 protected GillStateInterpolator createInterpolator(final boolean forward, final double[][] yDotK,
91 final ODEStateAndDerivative globalPreviousState,
92 final ODEStateAndDerivative globalCurrentState,
93 final EquationsMapper mapper) {
94 return new GillStateInterpolator(forward, yDotK, globalPreviousState, globalCurrentState,
95 globalPreviousState, globalCurrentState, mapper);
96 }
97
98 }