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  }