| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package org.apache.commons.math4.legacy.ode; |
| |
| import org.apache.commons.math4.legacy.core.jdkmath.AccurateMath; |
| |
| /** |
| * This class is used in the junit tests for the ODE integrators. |
| |
| * <p>This specific problem is the following differential equation : |
| * <pre> |
| * y' = -y |
| * </pre> |
| * the solution of this equation is a simple exponential function : |
| * <pre> |
| * y (t) = y (t0) exp (t0-t) |
| * </pre> |
| * </p> |
| |
| */ |
| public class TestProblem1 |
| extends TestProblemAbstract { |
| |
| /** theoretical state */ |
| private double[] y; |
| |
| /** |
| * Simple constructor. |
| */ |
| public TestProblem1() { |
| super(); |
| double[] y0 = { 1.0, 0.1 }; |
| setInitialConditions(0.0, y0); |
| setFinalConditions(4.0); |
| double[] errorScale = { 1.0, 1.0 }; |
| setErrorScale(errorScale); |
| y = new double[y0.length]; |
| } |
| |
| @Override |
| public void doComputeDerivatives(double t, double[] y, double[] yDot) { |
| |
| // compute the derivatives |
| for (int i = 0; i < getDimension(); ++i) { |
| yDot[i] = -y[i]; |
| } |
| |
| } |
| |
| @Override |
| public double[] computeTheoreticalState(double t) { |
| double c = AccurateMath.exp (getInitialTime() - t); |
| for (int i = 0; i < getDimension(); ++i) { |
| y[i] = c * getInitialState()[i]; |
| } |
| return y; |
| } |
| |
| } |