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