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' = -y
26 * </pre>
27 * the solution of this equation is a simple exponential function :
28 * <pre>
29 * y (t) = y (t0) exp (t0-t)
30 * </pre>
31 * </p>
32
33 */
34 public class TestProblem1
35 extends TestProblemAbstract {
36
37 /** Serializable version identifier. */
38 private static final long serialVersionUID = 1977870815289373164L;
39
40 /** theoretical state */
41 private double[] y;
42
43 /**
44 * Simple constructor.
45 */
46 public TestProblem1() {
47 super();
48 double[] y0 = { 1.0, 0.1 };
49 setInitialConditions(0.0, y0);
50 setFinalConditions(4.0);
51 double[] errorScale = { 1.0, 1.0 };
52 setErrorScale(errorScale);
53 y = new double[y0.length];
54 }
55
56 /**
57 * Copy constructor.
58 * @param problem problem to copy
59 */
60 public TestProblem1(TestProblem1 problem) {
61 super(problem);
62 y = problem.y.clone();
63 }
64
65 /** {@inheritDoc} */
66 public TestProblem1 copy() {
67 return new TestProblem1(this);
68 }
69
70 @Override
71 public void doComputeDerivatives(double t, double[] y, double[] yDot) {
72
73 // compute the derivatives
74 for (int i = 0; i < n; ++i)
75 yDot[i] = -y[i];
76
77 }
78
79 @Override
80 public double[] computeTheoreticalState(double t) {
81 double c = Math.exp (t0 - t);
82 for (int i = 0; i < n; ++i) {
83 y[i] = c * y0[i];
84 }
85 return y;
86 }
87
88 }