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 * http://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.apache.commons.math.ode;
19
20 /**
21 * This class is used in the junit tests for the ODE integrators.
22
23 * <p>This specific problem is the following differential equation :
24 * <pre>
25 * y' = t^3 - t y
26 * </pre>
27 * with the initial condition y (0) = 0. The solution of this equation
28 * is the following function :
29 * <pre>
30 * y (t) = t^2 + 2 (exp (- t^2 / 2) - 1)
31 * </pre>
32 * </p>
33
34 */
35 public class TestProblem2
36 extends TestProblemAbstract {
37
38 /** Serializable version identifier. */
39 private static final long serialVersionUID = 8330741783213512366L;
40
41 /** theoretical state */
42 private double[] y;
43
44 /**
45 * Simple constructor.
46 */
47 public TestProblem2() {
48 super();
49 double[] y0 = { 0.0 };
50 setInitialConditions(0.0, y0);
51 setFinalConditions(1.0);
52 double[] errorScale = { 1.0 };
53 setErrorScale(errorScale);
54 y = new double[y0.length];
55 }
56
57 /**
58 * Copy constructor.
59 * @param problem problem to copy
60 */
61 public TestProblem2(TestProblem2 problem) {
62 super(problem);
63 y = problem.y.clone();
64 }
65
66 /** {@inheritDoc} */
67 public TestProblem2 copy() {
68 return new TestProblem2(this);
69 }
70
71 @Override
72 public void doComputeDerivatives(double t, double[] y, double[] yDot) {
73
74 // compute the derivatives
75 for (int i = 0; i < n; ++i)
76 yDot[i] = t * (t * t - y[i]);
77
78 }
79
80 @Override
81 public double[] computeTheoreticalState(double t) {
82 double t2 = t * t;
83 double c = t2 + 2 * (Math.exp (-0.5 * t2) - 1);
84 for (int i = 0; i < n; ++i) {
85 y[i] = c;
86 }
87 return y;
88 }
89
90 }