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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    *      https://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  /*
19   * This is not the original file distributed by the Apache Software Foundation
20   * It has been modified by the Hipparchus project
21   */
22  
23  package org.hipparchus.ode;
24  
25  import org.hipparchus.Field;
26  import org.hipparchus.CalculusFieldElement;
27  import org.hipparchus.util.MathArrays;
28  
29  /**
30   * This class is used in the junit tests for the ODE integrators.
31  
32   * <p>This specific problem is the following differential equation :
33   * <pre>
34   *    y' = 3x^5 - y
35   * </pre>
36   * when the initial condition is y(0) = -360, the solution of this
37   * equation degenerates to a simple quintic polynomial function :
38   * <pre>
39   *   y (t) = 3x^5 - 15x^4 + 60x^3 - 180x^2 + 360x - 360
40   * </pre>
41   * </p>
42  
43   * @param <T> the type of the field elements
44   */
45  public class TestFieldProblem6<T extends CalculusFieldElement<T>>
46      extends TestFieldProblemAbstract<T> {
47  
48      /**
49       * Simple constructor.
50       * @param field field to which elements belong
51       */
52      public TestFieldProblem6(Field<T> field) {
53          super(convert(field, 0.0),
54                convert(field, new double[] { -360.0 }),
55                convert(field, 1.0),
56                convert(field, new double[] { 1.0 }));
57      }
58  
59      @Override
60      public T[] doComputeDerivatives(T t, T[] y) {
61  
62          final T[] yDot = MathArrays.buildArray(getField(), getDimension());
63  
64          // compute the derivatives
65          T t2 = t.multiply(t);
66          T t4 = t2.multiply(t2);
67          T t5 = t4.multiply(t);
68          for (int i = 0; i < getDimension(); ++i) {
69              yDot[i] = t5.multiply(3).subtract(y[i]);
70          }
71  
72          return yDot;
73  
74      }
75  
76      @Override
77      public T[] computeTheoreticalState(T t) {
78  
79          final T[] y = MathArrays.buildArray(getField(), getDimension());
80  
81          for (int i = 0; i < getDimension(); ++i) {
82              y[i] = t.multiply(3).subtract(15).multiply(t).add(60).multiply(t).subtract(180).multiply(t).add(360).multiply(t).subtract(360);
83          }
84  
85          return y;
86  
87      }
88  
89  }