| /* |
| * 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.math3.ode; |
| |
| import org.apache.commons.math3.ode.events.EventHandler; |
| import org.apache.commons.math3.util.FastMath; |
| |
| /** |
| * This class is used in the junit tests for the ODE integrators. |
| |
| * <p>This specific problem is the following differential equation : |
| * <pre> |
| * x'' = -x |
| * </pre> |
| * And when x decreases down to 0, the state should be changed as follows : |
| * <pre> |
| * x' -> -x' |
| * </pre> |
| * The theoretical solution of this problem is x = |sin(t+a)| |
| * </p> |
| |
| */ |
| public class TestProblem4 |
| extends TestProblemAbstract { |
| |
| /** Time offset. */ |
| private double a; |
| |
| /** theoretical state */ |
| private double[] y; |
| |
| /** Simple constructor. */ |
| public TestProblem4() { |
| super(); |
| a = 1.2; |
| double[] y0 = { FastMath.sin(a), FastMath.cos(a) }; |
| setInitialConditions(0.0, y0); |
| setFinalConditions(15); |
| double[] errorScale = { 1.0, 0.0 }; |
| setErrorScale(errorScale); |
| y = new double[y0.length]; |
| } |
| |
| @Override |
| public EventHandler[] getEventsHandlers() { |
| return new EventHandler[] { new Bounce(), new Stop() }; |
| } |
| |
| /** |
| * Get the theoretical events times. |
| * @return theoretical events times |
| */ |
| @Override |
| public double[] getTheoreticalEventsTimes() { |
| return new double[] { |
| 1 * FastMath.PI - a, |
| 2 * FastMath.PI - a, |
| 3 * FastMath.PI - a, |
| 4 * FastMath.PI - a, |
| 12.0 |
| }; |
| } |
| |
| @Override |
| public void doComputeDerivatives(double t, double[] y, double[] yDot) { |
| yDot[0] = y[1]; |
| yDot[1] = -y[0]; |
| } |
| |
| @Override |
| public double[] computeTheoreticalState(double t) { |
| double sin = FastMath.sin(t + a); |
| double cos = FastMath.cos(t + a); |
| y[0] = FastMath.abs(sin); |
| y[1] = (sin >= 0) ? cos : -cos; |
| return y; |
| } |
| |
| private static class Bounce implements EventHandler { |
| |
| private int sign; |
| |
| public Bounce() { |
| sign = +1; |
| } |
| |
| public void init(double t0, double[] y0, double t) { |
| } |
| |
| public double g(double t, double[] y) { |
| return sign * y[0]; |
| } |
| |
| public Action eventOccurred(double t, double[] y, boolean increasing) { |
| // this sign change is needed because the state will be reset soon |
| sign = -sign; |
| return Action.RESET_STATE; |
| } |
| |
| public void resetState(double t, double[] y) { |
| y[0] = -y[0]; |
| y[1] = -y[1]; |
| } |
| |
| } |
| |
| private static class Stop implements EventHandler { |
| |
| public Stop() { |
| } |
| |
| public void init(double t0, double[] y0, double t) { |
| } |
| |
| public double g(double t, double[] y) { |
| return t - 12.0; |
| } |
| |
| public Action eventOccurred(double t, double[] y, boolean increasing) { |
| return Action.STOP; |
| } |
| |
| public void resetState(double t, double[] y) { |
| } |
| |
| } |
| |
| } |