001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 018 package org.apache.commons.math.ode; 019 020 /** 021 * This class is used in the junit tests for the ODE integrators. 022 023 * <p>This specific problem is the following differential equation : 024 * <pre> 025 * y' = t^3 - t y 026 * </pre> 027 * with the initial condition y (0) = 0. The solution of this equation 028 * is the following function : 029 * <pre> 030 * y (t) = t^2 + 2 (exp (- t^2 / 2) - 1) 031 * </pre> 032 * </p> 033 034 */ 035 public class TestProblem2 036 extends TestProblemAbstract { 037 038 /** Serializable version identifier. */ 039 private static final long serialVersionUID = 8330741783213512366L; 040 041 /** theoretical state */ 042 private double[] y; 043 044 /** 045 * Simple constructor. 046 */ 047 public TestProblem2() { 048 super(); 049 double[] y0 = { 0.0 }; 050 setInitialConditions(0.0, y0); 051 setFinalConditions(1.0); 052 double[] errorScale = { 1.0 }; 053 setErrorScale(errorScale); 054 y = new double[y0.length]; 055 } 056 057 /** 058 * Copy constructor. 059 * @param problem problem to copy 060 */ 061 public TestProblem2(TestProblem2 problem) { 062 super(problem); 063 y = problem.y.clone(); 064 } 065 066 /** {@inheritDoc} */ 067 public TestProblem2 copy() { 068 return new TestProblem2(this); 069 } 070 071 @Override 072 public void doComputeDerivatives(double t, double[] y, double[] yDot) { 073 074 // compute the derivatives 075 for (int i = 0; i < n; ++i) 076 yDot[i] = t * (t * t - y[i]); 077 078 } 079 080 @Override 081 public double[] computeTheoreticalState(double t) { 082 double t2 = t * t; 083 double c = t2 + 2 * (Math.exp (-0.5 * t2) - 1); 084 for (int i = 0; i < n; ++i) { 085 y[i] = c; 086 } 087 return y; 088 } 089 090 }