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' = -y
28 * </pre>
29 * the solution of this equation is a simple exponential function :
30 * <pre>
31 * y (t) = y (t0) exp (t0-t)
32 * </pre>
33 * </p>
34
35 */
36 public class TestProblem1
37 extends TestProblemAbstract {
38
39 /** theoretical state */
40 private double[] y;
41
42 /**
43 * Simple constructor.
44 */
45 public TestProblem1() {
46 super();
47 double[] y0 = { 1.0, 0.1 };
48 setInitialConditions(0.0, y0);
49 setFinalConditions(4.0);
50 double[] errorScale = { 1.0, 1.0 };
51 setErrorScale(errorScale);
52 y = new double[y0.length];
53 }
54
55 @Override
56 public void doComputeDerivatives(double t, double[] y, double[] yDot) {
57
58 // compute the derivatives
59 for (int i = 0; i < getDimension(); ++i) {
60 yDot[i] = -y[i];
61 }
62 }
63
64 @Override
65 public double[] computeTheoreticalState(double t) {
66 double c = JdkMath.exp (getInitialTime() - t);
67 for (int i = 0; i < getDimension(); ++i) {
68 y[i] = c * getInitialState()[i];
69 }
70 return y;
71 }
72 }