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 (exp (- t^2 / 2) - 1) 31 * </pre> 32 * </p> 33 34 */ 35 public class TestProblem2 36 extends TestProblemAbstract { 37 38 /** Serializable version identifier. */ 39 private static final long serialVersionUID = 8330741783213512366L; 40 41 /** theoretical state */ 42 private double[] y; 43 44 /** 45 * Simple constructor. 46 */ 47 public TestProblem2() { 48 super(); 49 double[] y0 = { 0.0 }; 50 setInitialConditions(0.0, y0); 51 setFinalConditions(1.0); 52 double[] errorScale = { 1.0 }; 53 setErrorScale(errorScale); 54 y = new double[y0.length]; 55 } 56 57 /** 58 * Copy constructor. 59 * @param problem problem to copy 60 */ 61 public TestProblem2(TestProblem2 problem) { 62 super(problem); 63 y = problem.y.clone(); 64 } 65 66 /** {@inheritDoc} */ 67 public TestProblem2 copy() { 68 return new TestProblem2(this); 69 } 70 71 @Override 72 public void doComputeDerivatives(double t, double[] y, double[] yDot) { 73 74 // compute the derivatives 75 for (int i = 0; i < n; ++i) 76 yDot[i] = t * (t * t - y[i]); 77 78 } 79 80 @Override 81 public double[] computeTheoreticalState(double t) { 82 double t2 = t * t; 83 double c = t2 + 2 * (Math.exp (-0.5 * t2) - 1); 84 for (int i = 0; i < n; ++i) { 85 y[i] = c; 86 } 87 return y; 88 } 89 90 }