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.math4.legacy.ode;
19
20 import org.apache.commons.math4.core.jdkmath.JdkMath;
21
22 /**
23 * This class is used in the junit tests for the ODE integrators.
24
25 * <p>This specific problem is the following differential equation :
26 * <pre>
27 * y' = t^3 - t y
28 * </pre>
29 * with the initial condition y (0) = 0. The solution of this equation
30 * is the following function :
31 * <pre>
32 * y (t) = t^2 + 2 (exp (- t^2 / 2) - 1)
33 * </pre>
34 * </p>
35
36 */
37 public class TestProblem2
38 extends TestProblemAbstract {
39
40 /** theoretical state */
41 private double[] y;
42
43 /**
44 * Simple constructor.
45 */
46 public TestProblem2() {
47 super();
48 double[] y0 = { 0.0 };
49 setInitialConditions(0.0, y0);
50 setFinalConditions(1.0);
51 double[] errorScale = { 1.0 };
52 setErrorScale(errorScale);
53 y = new double[y0.length];
54 }
55
56 @Override
57 public void doComputeDerivatives(double t, double[] y, double[] yDot) {
58
59 // compute the derivatives
60 for (int i = 0; i < getDimension(); ++i) {
61 yDot[i] = t * (t * t - y[i]);
62 }
63 }
64
65 @Override
66 public double[] computeTheoreticalState(double t) {
67 double t2 = t * t;
68 double c = t2 + 2 * (JdkMath.exp (-0.5 * t2) - 1);
69 for (int i = 0; i < getDimension(); ++i) {
70 y[i] = c;
71 }
72 return y;
73 }
74 }