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.util.FastMath;
26
27 /**
28 * This class is used in the junit tests for the ODE integrators.
29 * <p>This is the same as problem 1 except integration is done
30 * backward in time</p>
31 */
32 public class TestProblem5 extends TestProblemAbstract {
33
34 /**
35 * Simple constructor.
36 */
37 public TestProblem5() {
38 super(0.0, new double[] { 1.0, 0.1 }, -4.0, new double[] { 1.0, 1.0 });
39 }
40
41 @Override
42 public double[] doComputeDerivatives(double t, double[] y) {
43
44 // compute the derivatives
45 final double[] yDot = new double[getDimension()];
46 for (int i = 0; i < getDimension(); ++i) {
47 yDot[i] = -y[i];
48 }
49 return yDot;
50
51 }
52
53 @Override
54 public double[] computeTheoreticalState(double t) {
55 final double c = FastMath.exp (getInitialTime() - t);
56 final double[] y = getInitialState().getPrimaryState();
57 for (int i = 0; i < getDimension(); ++i) {
58 y[i] *= c;
59 }
60 return y;
61 }
62
63 }