EventFilter.java
/*
* 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.
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package org.apache.commons.math4.legacy.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.math4.legacy.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} */
@Override
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} */
@Override
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} */
@Override
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} */
@Override
public void resetState(double t, double[] y) {
// delegate to raw handler
rawHandler.resetState(t, y);
}
}