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Java example source code file (AbstractFieldIntegrator.java)

This example Java source code file (AbstractFieldIntegrator.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.

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Java - Java tags/keywords

abstractfieldintegrator, abstractfieldstepinterpolator, arraylist, collection, dimensionmismatchexception, fieldeventhandler, fieldeventstate, fieldexpandableode, fieldodestateandderivative, fieldstephandler, iterator, maxcountexceededexception, string, util

The AbstractFieldIntegrator.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 java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.SortedSet;
import java.util.TreeSet;

import org.apache.commons.math3.Field;
import org.apache.commons.math3.RealFieldElement;
import org.apache.commons.math3.analysis.solvers.BracketedRealFieldUnivariateSolver;
import org.apache.commons.math3.analysis.solvers.FieldBracketingNthOrderBrentSolver;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.MaxCountExceededException;
import org.apache.commons.math3.exception.NoBracketingException;
import org.apache.commons.math3.exception.NumberIsTooSmallException;
import org.apache.commons.math3.exception.util.LocalizedFormats;
import org.apache.commons.math3.ode.events.FieldEventHandler;
import org.apache.commons.math3.ode.events.FieldEventState;
import org.apache.commons.math3.ode.sampling.AbstractFieldStepInterpolator;
import org.apache.commons.math3.ode.sampling.FieldStepHandler;
import org.apache.commons.math3.util.FastMath;
import org.apache.commons.math3.util.IntegerSequence;

/**
 * Base class managing common boilerplate for all integrators.
 * @param <T> the type of the field elements
 * @since 3.6
 */
public abstract class AbstractFieldIntegrator<T extends RealFieldElement implements FirstOrderFieldIntegrator {

    /** Default relative accuracy. */
    private static final double DEFAULT_RELATIVE_ACCURACY = 1e-14;

    /** Default function value accuracy. */
    private static final double DEFAULT_FUNCTION_VALUE_ACCURACY = 1e-15;

    /** Step handler. */
    private Collection<FieldStepHandler stepHandlers;

    /** Current step start. */
    private FieldODEStateAndDerivative<T> stepStart;

    /** Current stepsize. */
    private T stepSize;

    /** Indicator for last step. */
    private boolean isLastStep;

    /** Indicator that a state or derivative reset was triggered by some event. */
    private boolean resetOccurred;

    /** Field to which the time and state vector elements belong. */
    private final Field<T> field;

    /** Events states. */
    private Collection<FieldEventState eventsStates;

    /** Initialization indicator of events states. */
    private boolean statesInitialized;

    /** Name of the method. */
    private final String name;

    /** Counter for number of evaluations. */
    private IntegerSequence.Incrementor evaluations;

    /** Differential equations to integrate. */
    private transient FieldExpandableODE<T> equations;

    /** Build an instance.
     * @param field field to which the time and state vector elements belong
     * @param name name of the method
     */
    protected AbstractFieldIntegrator(final Field<T> field, final String name) {
        this.field        = field;
        this.name         = name;
        stepHandlers      = new ArrayList<FieldStepHandler();
        stepStart         = null;
        stepSize          = null;
        eventsStates      = new ArrayList<FieldEventState();
        statesInitialized = false;
        evaluations       = IntegerSequence.Incrementor.create().withMaximalCount(Integer.MAX_VALUE);
    }

    /** Get the field to which state vector elements belong.
     * @return field to which state vector elements belong
     */
    public Field<T> getField() {
        return field;
    }

    /** {@inheritDoc} */
    public String getName() {
        return name;
    }

    /** {@inheritDoc} */
    public void addStepHandler(final FieldStepHandler<T> handler) {
        stepHandlers.add(handler);
    }

    /** {@inheritDoc} */
    public Collection<FieldStepHandler getStepHandlers() {
        return Collections.unmodifiableCollection(stepHandlers);
    }

    /** {@inheritDoc} */
    public void clearStepHandlers() {
        stepHandlers.clear();
    }

    /** {@inheritDoc} */
    public void addEventHandler(final FieldEventHandler<T> handler,
                                final double maxCheckInterval,
                                final double convergence,
                                final int maxIterationCount) {
        addEventHandler(handler, maxCheckInterval, convergence,
                        maxIterationCount,
                        new FieldBracketingNthOrderBrentSolver<T>(field.getZero().add(DEFAULT_RELATIVE_ACCURACY),
                                                                  field.getZero().add(convergence),
                                                                  field.getZero().add(DEFAULT_FUNCTION_VALUE_ACCURACY),
                                                                  5));
    }

    /** {@inheritDoc} */
    public void addEventHandler(final FieldEventHandler<T> handler,
                                final double maxCheckInterval,
                                final double convergence,
                                final int maxIterationCount,
                                final BracketedRealFieldUnivariateSolver<T> solver) {
        eventsStates.add(new FieldEventState<T>(handler, maxCheckInterval, field.getZero().add(convergence),
                                                maxIterationCount, solver));
    }

    /** {@inheritDoc} */
    public Collection<FieldEventHandler getEventHandlers() {
        final List<FieldEventHandler list = new ArrayList>(eventsStates.size());
        for (FieldEventState<T> state : eventsStates) {
            list.add(state.getEventHandler());
        }
        return Collections.unmodifiableCollection(list);
    }

    /** {@inheritDoc} */
    public void clearEventHandlers() {
        eventsStates.clear();
    }

    /** {@inheritDoc} */
    public FieldODEStateAndDerivative<T> getCurrentStepStart() {
        return stepStart;
    }

    /** {@inheritDoc} */
    public T getCurrentSignedStepsize() {
        return stepSize;
    }

    /** {@inheritDoc} */
    public void setMaxEvaluations(int maxEvaluations) {
        evaluations = evaluations.withMaximalCount((maxEvaluations < 0) ? Integer.MAX_VALUE : maxEvaluations);
    }

    /** {@inheritDoc} */
    public int getMaxEvaluations() {
        return evaluations.getMaximalCount();
    }

    /** {@inheritDoc} */
    public int getEvaluations() {
        return evaluations.getCount();
    }

    /** Prepare the start of an integration.
     * @param eqn equations to integrate
     * @param t0 start value of the independent <i>time variable
     * @param y0 array containing the start value of the state vector
     * @param t target time for the integration
     * @return initial state with derivatives added
     */
    protected FieldODEStateAndDerivative<T> initIntegration(final FieldExpandableODE eqn,
                                                            final T t0, final T[] y0, final T t) {

        this.equations = eqn;
        evaluations    = evaluations.withStart(0);

        // initialize ODE
        eqn.init(t0, y0, t);

        // set up derivatives of initial state
        final T[] y0Dot = computeDerivatives(t0, y0);
        final FieldODEStateAndDerivative<T> state0 = new FieldODEStateAndDerivative(t0, y0, y0Dot);

        // initialize event handlers
        for (final FieldEventState<T> state : eventsStates) {
            state.getEventHandler().init(state0, t);
        }

        // initialize step handlers
        for (FieldStepHandler<T> handler : stepHandlers) {
            handler.init(state0, t);
        }

        setStateInitialized(false);

        return state0;

    }

    /** Get the differential equations to integrate.
     * @return differential equations to integrate
     */
    protected FieldExpandableODE<T> getEquations() {
        return equations;
    }

    /** Get the evaluations counter.
     * @return evaluations counter
     */
    protected IntegerSequence.Incrementor getEvaluationsCounter() {
        return evaluations;
    }

    /** Compute the derivatives and check the number of evaluations.
     * @param t current value of the independent <I>time variable
     * @param y array containing the current value of the state vector
     * @return state completed with derivatives
     * @exception DimensionMismatchException if arrays dimensions do not match equations settings
     * @exception MaxCountExceededException if the number of functions evaluations is exceeded
     * @exception NullPointerException if the ODE equations have not been set (i.e. if this method
     * is called outside of a call to {@link #integrate(FieldExpandableODE, FieldODEState,
     * RealFieldElement) integrate}
     */
    public T[] computeDerivatives(final T t, final T[] y)
        throws DimensionMismatchException, MaxCountExceededException, NullPointerException {
        evaluations.increment();
        return equations.computeDerivatives(t, y);
    }

    /** Set the stateInitialized flag.
     * <p>This method must be called by integrators with the value
     * {@code false} before they start integration, so a proper lazy
     * initialization is done automatically on the first step.</p>
     * @param stateInitialized new value for the flag
     */
    protected void setStateInitialized(final boolean stateInitialized) {
        this.statesInitialized = stateInitialized;
    }

    /** Accept a step, triggering events and step handlers.
     * @param interpolator step interpolator
     * @param tEnd final integration time
     * @return state at end of step
     * @exception MaxCountExceededException if the interpolator throws one because
     * the number of functions evaluations is exceeded
     * @exception NoBracketingException if the location of an event cannot be bracketed
     * @exception DimensionMismatchException if arrays dimensions do not match equations settings
     */
    protected FieldODEStateAndDerivative<T> acceptStep(final AbstractFieldStepInterpolator interpolator,
                                                       final T tEnd)
        throws MaxCountExceededException, DimensionMismatchException, NoBracketingException {

            FieldODEStateAndDerivative<T> previousState = interpolator.getGlobalPreviousState();
            final FieldODEStateAndDerivative<T> currentState = interpolator.getGlobalCurrentState();

            // initialize the events states if needed
            if (! statesInitialized) {
                for (FieldEventState<T> state : eventsStates) {
                    state.reinitializeBegin(interpolator);
                }
                statesInitialized = true;
            }

            // search for next events that may occur during the step
            final int orderingSign = interpolator.isForward() ? +1 : -1;
            SortedSet<FieldEventState occurringEvents = new TreeSet>(new Comparator>() {

                /** {@inheritDoc} */
                public int compare(FieldEventState<T> es0, FieldEventState es1) {
                    return orderingSign * Double.compare(es0.getEventTime().getReal(), es1.getEventTime().getReal());
                }

            });

            for (final FieldEventState<T> state : eventsStates) {
                if (state.evaluateStep(interpolator)) {
                    // the event occurs during the current step
                    occurringEvents.add(state);
                }
            }

            AbstractFieldStepInterpolator<T> restricted = interpolator;
            while (!occurringEvents.isEmpty()) {

                // handle the chronologically first event
                final Iterator<FieldEventState iterator = occurringEvents.iterator();
                final FieldEventState<T> currentEvent = iterator.next();
                iterator.remove();

                // get state at event time
                final FieldODEStateAndDerivative<T> eventState = restricted.getInterpolatedState(currentEvent.getEventTime());

                // restrict the interpolator to the first part of the step, up to the event
                restricted = restricted.restrictStep(previousState, eventState);

                // advance all event states to current time
                for (final FieldEventState<T> state : eventsStates) {
                    state.stepAccepted(eventState);
                    isLastStep = isLastStep || state.stop();
                }

                // handle the first part of the step, up to the event
                for (final FieldStepHandler<T> handler : stepHandlers) {
                    handler.handleStep(restricted, isLastStep);
                }

                if (isLastStep) {
                    // the event asked to stop integration
                    return eventState;
                }

                FieldODEState<T> newState = null;
                resetOccurred = false;
                for (final FieldEventState<T> state : eventsStates) {
                    newState = state.reset(eventState);
                    if (newState != null) {
                        // some event handler has triggered changes that
                        // invalidate the derivatives, we need to recompute them
                        final T[] y    = equations.getMapper().mapState(newState);
                        final T[] yDot = computeDerivatives(newState.getTime(), y);
                        resetOccurred = true;
                        return equations.getMapper().mapStateAndDerivative(newState.getTime(), y, yDot);
                    }
                }

                // prepare handling of the remaining part of the step
                previousState = eventState;
                restricted = restricted.restrictStep(eventState, currentState);

                // check if the same event occurs again in the remaining part of the step
                if (currentEvent.evaluateStep(restricted)) {
                    // the event occurs during the current step
                    occurringEvents.add(currentEvent);
                }

            }

            // last part of the step, after the last event
            for (final FieldEventState<T> state : eventsStates) {
                state.stepAccepted(currentState);
                isLastStep = isLastStep || state.stop();
            }
            isLastStep = isLastStep || currentState.getTime().subtract(tEnd).abs().getReal() <= FastMath.ulp(tEnd.getReal());

            // handle the remaining part of the step, after all events if any
            for (FieldStepHandler<T> handler : stepHandlers) {
                handler.handleStep(restricted, isLastStep);
            }

            return currentState;

    }

    /** Check the integration span.
     * @param eqn set of differential equations
     * @param t target time for the integration
     * @exception NumberIsTooSmallException if integration span is too small
     * @exception DimensionMismatchException if adaptive step size integrators
     * tolerance arrays dimensions are not compatible with equations settings
     */
    protected void sanityChecks(final FieldODEState<T> eqn, final T t)
        throws NumberIsTooSmallException, DimensionMismatchException {

        final double threshold = 1000 * FastMath.ulp(FastMath.max(FastMath.abs(eqn.getTime().getReal()),
                                                                  FastMath.abs(t.getReal())));
        final double dt = eqn.getTime().subtract(t).abs().getReal();
        if (dt <= threshold) {
            throw new NumberIsTooSmallException(LocalizedFormats.TOO_SMALL_INTEGRATION_INTERVAL,
                                                dt, threshold, false);
        }

    }

    /** Check if a reset occurred while last step was accepted.
     * @return true if a reset occurred while last step was accepted
     */
    protected boolean resetOccurred() {
        return resetOccurred;
    }

    /** Set the current step size.
     * @param stepSize step size to set
     */
    protected void setStepSize(final T stepSize) {
        this.stepSize = stepSize;
    }

    /** Get the current step size.
     * @return current step size
     */
    protected T getStepSize() {
        return stepSize;
    }
    /** Set current step start.
     * @param stepStart step start
     */
    protected void setStepStart(final FieldODEStateAndDerivative<T> stepStart) {
        this.stepStart = stepStart;
    }

    /** Getcurrent step start.
     * @return current step start
     */
    protected FieldODEStateAndDerivative<T> getStepStart() {
        return stepStart;
    }

    /** Set the last state flag.
     * @param isLastStep if true, this step is the last one
     */
    protected void setIsLastStep(final boolean isLastStep) {
        this.isLastStep = isLastStep;
    }

    /** Check if this step is the last one.
     * @return true if this step is the last one
     */
    protected boolean isLastStep() {
        return isLastStep;
    }

}

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