1 /*
2 * Licensed to the Apache Software Foundation (ASF) 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 ASF 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 /*
19 * This is not the original file distributed by the Apache Software Foundation
20 * It has been modified by the Hipparchus project
21 */
22
23 package org.hipparchus.ode;
24
25 /**
26 * This class is used in the junit tests for the ODE integrators.
27
28 * <p>This specific problem is the following differential equation :
29 * <pre>
30 * y' = 3x^5 - y
31 * </pre>
32 * when the initial condition is y(0) = -360, the solution of this
33 * equation degenerates to a simple quintic polynomial function :
34 * <pre>
35 * y (t) = 3x^5 - 15x^4 + 60x^3 - 180x^2 + 360x - 360
36 * </pre>
37 * </p>
38
39 */
40 public class TestProblem6 extends TestProblemAbstract {
41
42 /**
43 * Simple constructor.
44 */
45 public TestProblem6() {
46 super(0.0, new double[] { -360.0 }, 1.0, new double[] { 1.0 });
47 }
48
49 @Override
50 public double[] doComputeDerivatives(double t, double[] y) {
51
52 final double[] yDot = new double[getDimension()];
53
54 // compute the derivatives
55 double t2 = t * t;
56 double t4 = t2 * t2;
57 double t5 = t4 * t;
58 for (int i = 0; i < getDimension(); ++i) {
59 yDot[i] = 3 * t5 - y[i];
60 }
61
62 return yDot;
63
64 }
65
66 @Override
67 public double[] computeTheoreticalState(double t) {
68 final double[] y = new double[getDimension()];
69 for (int i = 0; i < getDimension(); ++i) {
70 y[i] = ((((3 * t - 15) * t + 60) * t - 180) * t + 360) * t - 360;
71 }
72 return y;
73 }
74
75 }