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 * <p>This is the same as problem 1 except integration is done
32 * backward in time</p>
33 * @param <T> the type of the field elements
34 */
35 public class TestFieldProblem5<T extends CalculusFieldElement<T>>
36 extends TestFieldProblemAbstract<T> {
37
38 /**
39 * Simple constructor.
40 * @param field field to which elements belong
41 */
42 public TestFieldProblem5(Field<T> field) {
43 super(convert(field, 0.0),
44 convert(field, 1.0, 0.1),
45 convert(field, -4.0),
46 convert(field, 1.0, 1.0));
47 }
48
49 @Override
50 public T[] doComputeDerivatives(T t, T[] y) {
51
52 final T[] yDot = MathArrays.buildArray(getField(), getDimension());
53
54 // compute the derivatives
55 for (int i = 0; i < getDimension(); ++i) {
56 yDot[i] = y[i].negate();
57 }
58
59 return yDot;
60
61 }
62
63 @Override
64 public T[] computeTheoreticalState(T t) {
65 final FieldODEState<T> s0 = getInitialState();
66 final T[] y0 = s0.getPrimaryState();
67 final T[] y = MathArrays.buildArray(getField(), getDimension());
68 T c = s0.getTime().subtract(t).exp();
69 for (int i = 0; i < getDimension(); ++i) {
70 y[i] = c.multiply(y0[i]);
71 }
72 return y;
73 }
74
75 }