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' = -y 26 * </pre> 27 * the solution of this equation is a simple exponential function : 28 * <pre> 29 * y (t) = y (t0) exp (t0-t) 30 * </pre> 31 * </p> 32 33 */ 34 public class TestProblem1 35 extends TestProblemAbstract { 36 37 /** Serializable version identifier. */ 38 private static final long serialVersionUID = 1977870815289373164L; 39 40 /** theoretical state */ 41 private double[] y; 42 43 /** 44 * Simple constructor. 45 */ 46 public TestProblem1() { 47 super(); 48 double[] y0 = { 1.0, 0.1 }; 49 setInitialConditions(0.0, y0); 50 setFinalConditions(4.0); 51 double[] errorScale = { 1.0, 1.0 }; 52 setErrorScale(errorScale); 53 y = new double[y0.length]; 54 } 55 56 /** 57 * Copy constructor. 58 * @param problem problem to copy 59 */ 60 public TestProblem1(TestProblem1 problem) { 61 super(problem); 62 y = problem.y.clone(); 63 } 64 65 /** {@inheritDoc} */ 66 public TestProblem1 copy() { 67 return new TestProblem1(this); 68 } 69 70 @Override 71 public void doComputeDerivatives(double t, double[] y, double[] yDot) { 72 73 // compute the derivatives 74 for (int i = 0; i < n; ++i) 75 yDot[i] = -y[i]; 76 77 } 78 79 @Override 80 public double[] computeTheoreticalState(double t) { 81 double c = Math.exp (t0 - t); 82 for (int i = 0; i < n; ++i) { 83 y[i] = c * y0[i]; 84 } 85 return y; 86 } 87 88 }