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' = 3x^5 - y
26   * </pre>
27   * when the initial condition is y(0) = -360, the solution of this
28   * equation degenerates to a simple quintic polynomial function :
29   * <pre>
30   *   y (t) = 3x^5 - 15x^4 + 60x^3 - 180x^2 + 360x - 360
31   * </pre>
32   * </p>
33  
34   */
35  public class TestProblem6
36    extends TestProblemAbstract {
37  
38      /** Serializable version identifier. */
39      private static final long serialVersionUID = 1353409119804352378L;
40  
41      /** theoretical state */
42      private double[] y;
43  
44      /**
45       * Simple constructor.
46       */
47      public TestProblem6() {
48          super();
49          double[] y0 = { -360.0 };
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 TestProblem6(TestProblem6 problem) {
62          super(problem);
63          y = problem.y.clone();
64      }
65  
66      /** {@inheritDoc} */
67      public TestProblem6 copy() {
68        return new TestProblem6(this);
69      }
70  
71      @Override
72      public void doComputeDerivatives(double t, double[] y, double[] yDot) {
73  
74          // compute the derivatives
75          double t2 = t  * t;
76          double t4 = t2 * t2;
77          double t5 = t4 * t;
78          for (int i = 0; i < n; ++i) {
79              yDot[i] = 3 * t5 - y[i];
80          }
81  
82      }
83  
84      @Override
85      public double[] computeTheoreticalState(double t) {
86          for (int i = 0; i < n; ++i) {
87              y[i] = ((((3 * t - 15) * t + 60) * t - 180) * t + 360) * t - 360;
88          }
89          return y;
90      }
91  
92  }