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 class TestProblem1 35 extends TestProblemAbstract { 36 37 /** theoretical state */ 38 private double[] y; 39 40 /** 41 * Simple constructor. 42 */ 43 public TestProblem1() { 44 super(); 45 double[] y0 = { 1.0, 0.1 }; 46 setInitialConditions(0.0, y0); 47 setFinalConditions(4.0); 48 double[] errorScale = { 1.0, 1.0 }; 49 setErrorScale(errorScale); 50 y = new double[y0.length]; 51 } 52 53 /** 54 * Copy constructor. 55 * @param problem problem to copy 56 */ 57 public TestProblem1(TestProblem1 problem) { 58 super(problem); 59 y = (double[]) problem.y.clone(); 60 } 61 62 /** 63 * Clone operation. 64 * @return a copy of the instance 65 */ 66 public Object clone() { 67 return new TestProblem1(this); 68 } 69 70 public void doComputeDerivatives(double t, double[] y, double[] yDot) { 71 72 // compute the derivatives 73 for (int i = 0; i < n; ++i) 74 yDot[i] = -y[i]; 75 76 } 77 78 public double[] computeTheoreticalState(double t) { 79 double c = Math.exp (t0 - t); 80 for (int i = 0; i < n; ++i) { 81 y[i] = c * y0[i]; 82 } 83 return y; 84 } 85 86 }