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Java example source code file (TestProblem4.java)

This example Java source code file (TestProblem4.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

action, bounce, eventhandler, override, stop, testproblem4, testproblemabstract

The TestProblem4.java Java example source code

/*
 * 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) {
    }

  }

}

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