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' = -y
35 * </pre>
36 * the solution of this equation is a simple exponential function :
37 * <pre>
38 * y (t) = y (t0) exp (t0-t)
39 * </pre>
40 * </p>
41
42 * @param <T> the type of the field elements
43 */
44 public class TestFieldProblem1<T extends CalculusFieldElement<T>>
45 extends TestFieldProblemAbstract<T> {
46
47 /**
48 * Simple constructor.
49 * @param field field to which elements belong
50 */
51 public TestFieldProblem1(Field<T> field) {
52 super(convert(field, 0.0),
53 convert(field, 1.0, 0.1),
54 convert(field, 4.0),
55 convert(field, 1.0, 1.0));
56 }
57
58 @Override
59 public T[] doComputeDerivatives(T t, T[] y) {
60
61 final T[] yDot = MathArrays.buildArray(getField(), getDimension());
62
63 // compute the derivatives
64 for (int i = 0; i < getDimension(); ++i) {
65 yDot[i] = y[i].negate();
66 }
67
68 return yDot;
69
70 }
71
72 @Override
73 public T[] computeTheoreticalState(T t) {
74 final FieldODEState<T> s0 = getInitialState();
75 final T[] y0 = s0.getPrimaryState();
76 final T[] y = MathArrays.buildArray(getField(), getDimension());
77 T c = s0.getTime().subtract(t).exp();
78 for (int i = 0; i < getDimension(); ++i) {
79 y[i] = c.multiply(y0[i]);
80 }
81 return y;
82 }
83
84 }