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Java example source code file (TestFieldProblem4.java)

This example Java source code file (TestFieldProblem4.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, fieldeventhandler, fieldodestate, override, realfieldelement, reflection, stop, suppresswarnings, testfieldproblem4, testfieldproblemabstract

The TestFieldProblem4.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,
 * See the License for the specific language governing permissions and
 * limitations under the License.

package org.apache.commons.math3.ode;

import java.lang.reflect.Array;

import org.apache.commons.math3.Field;
import org.apache.commons.math3.RealFieldElement;
import org.apache.commons.math3.ode.events.Action;
import org.apache.commons.math3.ode.events.FieldEventHandler;
import org.apache.commons.math3.util.FastMath;
import org.apache.commons.math3.util.MathArrays;

 * 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>

 * @param <T> the type of the field elements
public class TestFieldProblem4<T extends RealFieldElement
    extends TestFieldProblemAbstract<T> {

    /** Time offset. */
    private T a;

    /** Simple constructor.
     * @param field field to which elements belong
    public TestFieldProblem4(Field<T> field) {
        a = convert(1.2);
        T[] y0 = MathArrays.buildArray(field, 2);
        y0[0] = a.sin();
        y0[1] = a.cos();;
        setInitialConditions(convert(0.0), y0);
        setErrorScale(convert(1.0, 0.0));

    public FieldEventHandler<T>[] getEventsHandlers() {
        FieldEventHandler<T>[] handlers =
                        (FieldEventHandler<T>[]) Array.newInstance(FieldEventHandler.class, 2);
        handlers[0] = new Bounce<T>();
        handlers[1] = new Stop<T>();
        return handlers;

     * Get the theoretical events times.
     * @return theoretical events times
    public T[] getTheoreticalEventsTimes() {
        T[] array = MathArrays.buildArray(getField(), 5);
        array[0] = a.negate().add(1 * FastMath.PI);
        array[1] = a.negate().add(2 * FastMath.PI);
        array[2] = a.negate().add(3 * FastMath.PI);
        array[3] = a.negate().add(4 * FastMath.PI);
        array[4] = convert(120.0);
        return array;

    public T[] doComputeDerivatives(T t, T[] y) {
        final T[] yDot = MathArrays.buildArray(getField(), getDimension());
        yDot[0] = y[1];
        yDot[1] = y[0].negate();
        return yDot;

    public T[] computeTheoreticalState(T t) {
        T sin = t.add(a).sin();
        T cos = t.add(a).cos();
        final T[] y = MathArrays.buildArray(getField(), getDimension());
        y[0] = sin.abs();
        y[1] = (sin.getReal() >= 0) ? cos : cos.negate();
        return y;

    private static class Bounce<T extends RealFieldElement implements FieldEventHandler {

        private int sign;

        public Bounce() {
            sign = +1;

        public void init(FieldODEStateAndDerivative<T> state0, T t) {

        public T g(FieldODEStateAndDerivative<T> state) {
            return state.getState()[0].multiply(sign);

        public Action eventOccurred(FieldODEStateAndDerivative<T> state, boolean increasing) {
            // this sign change is needed because the state will be reset soon
            sign = -sign;
            return Action.RESET_STATE;

        public FieldODEState<T> resetState(FieldODEStateAndDerivative state) {
            T[] y = state.getState();
            y[0] = y[0].negate();
            y[1] = y[1].negate();
            return new FieldODEState<T>(state.getTime(), y);


    private static class Stop<T extends RealFieldElement implements FieldEventHandler {

        public Stop() {

        public void init(FieldODEStateAndDerivative<T> state0, T t) {

        public T g(FieldODEStateAndDerivative<T> state) {
            return state.getTime().subtract(12.0);

        public Action eventOccurred(FieldODEStateAndDerivative<T> state, boolean increasing) {
            return Action.STOP;

        public FieldODEState<T> resetState(FieldODEStateAndDerivative state) {
            return state;



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