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Java example source code file (EventFilter.java)

This example Java source code file (EventFilter.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, eventfilter, eventhandler, filtertype, history_size, transformer, util

The EventFilter.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.events;

import java.util.Arrays;

/** Wrapper used to detect only increasing or decreasing events.
 *
 * <p>General {@link EventHandler events} are defined implicitly
 * by a {@link EventHandler#g(double, double[]) g function} crossing
 * zero. This function needs to be continuous in the event neighborhood,
 * and its sign must remain consistent between events. This implies that
 * during an ODE integration, events triggered are alternately events
 * for which the function increases from negative to positive values,
 * and events for which the function decreases from positive to
 * negative values.
 * </p>
 *
 * <p>Sometimes, users are only interested in one type of event (say
 * increasing events for example) and not in the other type. In these
 * cases, looking precisely for all events location and triggering
 * events that will later be ignored is a waste of computing time.</p>
 *
 * <p>Users can wrap a regular {@link EventHandler event handler} in
 * an instance of this class and provide this wrapping instance to
 * the {@link org.apache.commons.math3.ode.FirstOrderIntegrator ODE solver}
 * in order to avoid wasting time looking for uninteresting events.
 * The wrapper will intercept the calls to the {@link
 * EventHandler#g(double, double[]) g function} and to the {@link
 * EventHandler#eventOccurred(double, double[], boolean)
 * eventOccurred} method in order to ignore uninteresting events. The
 * wrapped regular {@link EventHandler event handler} will the see only
 * the interesting events, i.e. either only {@code increasing} events or
 * {@code decreasing} events. the number of calls to the {@link
 * EventHandler#g(double, double[]) g function} will also be reduced.</p>
 *
 * @since 3.2
 */

public class EventFilter implements EventHandler {

    /** Number of past transformers updates stored. */
    private static final int HISTORY_SIZE = 100;

    /** Wrapped event handler. */
    private final EventHandler rawHandler;

    /** Filter to use. */
    private final FilterType filter;

    /** Transformers of the g function. */
    private final Transformer[] transformers;

    /** Update time of the transformers. */
    private final double[] updates;

    /** Indicator for forward integration. */
    private boolean forward;

    /** Extreme time encountered so far. */
    private double extremeT;

    /** Wrap an {@link EventHandler event handler}.
     * @param rawHandler event handler to wrap
     * @param filter filter to use
     */
    public EventFilter(final EventHandler rawHandler, final FilterType filter) {
        this.rawHandler   = rawHandler;
        this.filter       = filter;
        this.transformers = new Transformer[HISTORY_SIZE];
        this.updates      = new double[HISTORY_SIZE];
    }

    /**  {@inheritDoc} */
    public void init(double t0, double[] y0, double t) {

        // delegate to raw handler
        rawHandler.init(t0, y0, t);

        // initialize events triggering logic
        forward  = t >= t0;
        extremeT = forward ? Double.NEGATIVE_INFINITY : Double.POSITIVE_INFINITY;
        Arrays.fill(transformers, Transformer.UNINITIALIZED);
        Arrays.fill(updates, extremeT);

    }

    /**  {@inheritDoc} */
    public double g(double t, double[] y) {

        final double rawG = rawHandler.g(t, y);

        // search which transformer should be applied to g
        if (forward) {
            final int last = transformers.length - 1;
            if (extremeT < t) {
                // we are at the forward end of the history

                // check if a new rough root has been crossed
                final Transformer previous = transformers[last];
                final Transformer next     = filter.selectTransformer(previous, rawG, forward);
                if (next != previous) {
                    // there is a root somewhere between extremeT and t.
                    // the new transformer is valid for t (this is how we have just computed
                    // it above), but it is in fact valid on both sides of the root, so
                    // it was already valid before t and even up to previous time. We store
                    // the switch at extremeT for safety, to ensure the previous transformer
                    // is not applied too close of the root
                    System.arraycopy(updates,      1, updates,      0, last);
                    System.arraycopy(transformers, 1, transformers, 0, last);
                    updates[last]      = extremeT;
                    transformers[last] = next;
                }

                extremeT = t;

                // apply the transform
                return next.transformed(rawG);

            } else {
                // we are in the middle of the history

                // select the transformer
                for (int i = last; i > 0; --i) {
                    if (updates[i] <= t) {
                        // apply the transform
                        return transformers[i].transformed(rawG);
                    }
                }

                return transformers[0].transformed(rawG);

            }
        } else {
            if (t < extremeT) {
                // we are at the backward end of the history

                // check if a new rough root has been crossed
                final Transformer previous = transformers[0];
                final Transformer next     = filter.selectTransformer(previous, rawG, forward);
                if (next != previous) {
                    // there is a root somewhere between extremeT and t.
                    // the new transformer is valid for t (this is how we have just computed
                    // it above), but it is in fact valid on both sides of the root, so
                    // it was already valid before t and even up to previous time. We store
                    // the switch at extremeT for safety, to ensure the previous transformer
                    // is not applied too close of the root
                    System.arraycopy(updates,      0, updates,      1, updates.length - 1);
                    System.arraycopy(transformers, 0, transformers, 1, transformers.length - 1);
                    updates[0]      = extremeT;
                    transformers[0] = next;
                }

                extremeT = t;

                // apply the transform
                return next.transformed(rawG);

            } else {
                // we are in the middle of the history

                // select the transformer
                for (int i = 0; i < updates.length - 1; ++i) {
                    if (t <= updates[i]) {
                        // apply the transform
                        return transformers[i].transformed(rawG);
                    }
                }

                return transformers[updates.length - 1].transformed(rawG);

            }
       }

    }

    /**  {@inheritDoc} */
    public Action eventOccurred(double t, double[] y, boolean increasing) {
        // delegate to raw handler, fixing increasing status on the fly
        return rawHandler.eventOccurred(t, y, filter.getTriggeredIncreasing());
    }

    /**  {@inheritDoc} */
    public void resetState(double t, double[] y) {
        // delegate to raw handler
        rawHandler.resetState(t, y);
    }

}

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