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' = t^3 - t y 26 * </pre> 27 * with the initial condition y (0) = 0. The solution of this equation 28 * is the following function : 29 * <pre> 30 * y (t) = t^2 + 2 (ext (- t^2 / 2) - 1) 31 * </pre> 32 * </p> 33 34 */ 35 class TestProblem2 36 extends TestProblemAbstract { 37 38 /** theoretical state */ 39 private double[] y; 40 41 /** 42 * Simple constructor. 43 */ 44 public TestProblem2() { 45 super(); 46 double[] y0 = { 0.0 }; 47 setInitialConditions(0.0, y0); 48 setFinalConditions(1.0); 49 double[] errorScale = { 1.0 }; 50 setErrorScale(errorScale); 51 y = new double[y0.length]; 52 } 53 54 /** 55 * Copy constructor. 56 * @param problem problem to copy 57 */ 58 public TestProblem2(TestProblem2 problem) { 59 super(problem); 60 y = (double[]) problem.y.clone(); 61 } 62 63 /** 64 * Clone operation. 65 * @return a copy of the instance 66 */ 67 public Object clone() { 68 return new TestProblem2(this); 69 } 70 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] = t * (t * t - y[i]); 76 77 } 78 79 public double[] computeTheoreticalState(double t) { 80 double t2 = t * t; 81 double c = t2 + 2 * (Math.exp (-0.5 * t2) - 1); 82 for (int i = 0; i < n; ++i) { 83 y[i] = c; 84 } 85 return y; 86 } 87 88 }