EventState.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.
- */
- package org.orekit.propagation.events;
- import org.hipparchus.analysis.UnivariateFunction;
- import org.hipparchus.analysis.solvers.BracketedUnivariateSolver;
- import org.hipparchus.analysis.solvers.BracketedUnivariateSolver.Interval;
- import org.hipparchus.analysis.solvers.BracketingNthOrderBrentSolver;
- import org.hipparchus.exception.MathRuntimeException;
- import org.hipparchus.ode.events.Action;
- import org.hipparchus.util.FastMath;
- import org.hipparchus.util.Precision;
- import org.orekit.errors.OrekitException;
- import org.orekit.errors.OrekitInternalError;
- import org.orekit.errors.OrekitMessages;
- import org.orekit.propagation.SpacecraftState;
- import org.orekit.propagation.sampling.OrekitStepInterpolator;
- import org.orekit.time.AbsoluteDate;
- /** This class handles the state for one {@link EventDetector
- * event detector} during integration steps.
- *
- * <p>This class is heavily based on the class with the same name from the
- * Hipparchus library. The changes performed consist in replacing
- * raw types (double and double arrays) with space dynamics types
- * ({@link AbsoluteDate}, {@link SpacecraftState}).</p>
- * <p>Each time the propagator proposes a step, the event detector
- * should be checked. This class handles the state of one detector
- * during one propagation step, with references to the state at the
- * end of the preceding step. This information is used to determine if
- * the detector should trigger an event or not during the proposed
- * step (and hence the step should be reduced to ensure the event
- * occurs at a bound rather than inside the step).</p>
- * @author Luc Maisonobe
- * @param <T> class type for the generic version
- */
- public class EventState<T extends EventDetector> {
- /** Event detector. */
- private T detector;
- /** Time of the previous call to g. */
- private AbsoluteDate lastT;
- /** Value from the previous call to g. */
- private double lastG;
- /** Time at the beginning of the step. */
- private AbsoluteDate t0;
- /** Value of the event detector at the beginning of the step. */
- private double g0;
- /** Simulated sign of g0 (we cheat when crossing events). */
- private boolean g0Positive;
- /** Indicator of event expected during the step. */
- private boolean pendingEvent;
- /** Occurrence time of the pending event. */
- private AbsoluteDate pendingEventTime;
- /**
- * Time to stop propagation if the event is a stop event. Used to enable stopping at
- * an event and then restarting after that event.
- */
- private AbsoluteDate stopTime;
- /** Time after the current event. */
- private AbsoluteDate afterEvent;
- /** Value of the g function after the current event. */
- private double afterG;
- /** The earliest time considered for events. */
- private AbsoluteDate earliestTimeConsidered;
- /** Integration direction. */
- private boolean forward;
- /** Variation direction around pending event.
- * (this is considered with respect to the integration direction)
- */
- private boolean increasing;
- /** Simple constructor.
- * @param detector monitored event detector
- */
- public EventState(final T detector) {
- this.detector = detector;
- // some dummy values ...
- lastT = AbsoluteDate.PAST_INFINITY;
- lastG = Double.NaN;
- t0 = null;
- g0 = Double.NaN;
- g0Positive = true;
- pendingEvent = false;
- pendingEventTime = null;
- stopTime = null;
- increasing = true;
- earliestTimeConsidered = null;
- afterEvent = null;
- afterG = Double.NaN;
- }
- /** Get the underlying event detector.
- * @return underlying event detector
- */
- public T getEventDetector() {
- return detector;
- }
- /** Initialize event handler at the start of a propagation.
- * <p>
- * This method is called once at the start of the propagation. It
- * may be used by the event handler to initialize some internal data
- * if needed.
- * </p>
- * @param s0 initial state
- * @param t target time for the integration
- *
- */
- public void init(final SpacecraftState s0,
- final AbsoluteDate t) {
- detector.init(s0, t);
- lastT = AbsoluteDate.PAST_INFINITY;
- lastG = Double.NaN;
- }
- /** Compute the value of the switching function.
- * This function must be continuous (at least in its roots neighborhood),
- * as the integrator will need to find its roots to locate the events.
- * @param s the current state information: date, kinematics, attitude
- * @return value of the switching function
- */
- private double g(final SpacecraftState s) {
- if (!s.getDate().equals(lastT)) {
- lastG = detector.g(s);
- lastT = s.getDate();
- }
- return lastG;
- }
- /** Reinitialize the beginning of the step.
- * @param interpolator interpolator valid for the current step
- */
- public void reinitializeBegin(final OrekitStepInterpolator interpolator) {
- forward = interpolator.isForward();
- final SpacecraftState s0 = interpolator.getPreviousState();
- this.t0 = s0.getDate();
- g0 = g(s0);
- while (g0 == 0) {
- // extremely rare case: there is a zero EXACTLY at interval start
- // we will use the sign slightly after step beginning to force ignoring this zero
- // try moving forward by half a convergence interval
- final double dt = (forward ? 0.5 : -0.5) * detector.getThreshold();
- AbsoluteDate startDate = t0.shiftedBy(dt);
- // if convergence is too small move an ulp
- if (t0.equals(startDate)) {
- startDate = nextAfter(startDate);
- }
- t0 = startDate;
- g0 = g(interpolator.getInterpolatedState(t0));
- }
- g0Positive = g0 > 0;
- // "last" event was increasing
- increasing = g0Positive;
- }
- /** Evaluate the impact of the proposed step on the event detector.
- * @param interpolator step interpolator for the proposed step
- * @return true if the event detector triggers an event before
- * the end of the proposed step (this implies the step should be
- * rejected)
- * @exception MathRuntimeException if an event cannot be located
- */
- public boolean evaluateStep(final OrekitStepInterpolator interpolator)
- throws MathRuntimeException {
- forward = interpolator.isForward();
- final SpacecraftState s1 = interpolator.getCurrentState();
- final AbsoluteDate t1 = s1.getDate();
- final double dt = t1.durationFrom(t0);
- if (FastMath.abs(dt) < detector.getThreshold()) {
- // we cannot do anything on such a small step, don't trigger any events
- return false;
- }
- // number of points to check in the current step
- final int n = FastMath.max(1, (int) FastMath.ceil(FastMath.abs(dt) / detector.getMaxCheckInterval()));
- final double h = dt / n;
- AbsoluteDate ta = t0;
- double ga = g0;
- for (int i = 0; i < n; ++i) {
- // evaluate handler value at the end of the substep
- final AbsoluteDate tb = (i == n - 1) ? t1 : t0.shiftedBy((i + 1) * h);
- final double gb = g(interpolator.getInterpolatedState(tb));
- // check events occurrence
- if (gb == 0.0 || (g0Positive ^ (gb > 0))) {
- // there is a sign change: an event is expected during this step
- if (findRoot(interpolator, ta, ga, tb, gb)) {
- return true;
- }
- } else {
- // no sign change: there is no event for now
- ta = tb;
- ga = gb;
- }
- }
- // no event during the whole step
- pendingEvent = false;
- pendingEventTime = null;
- return false;
- }
- /**
- * Find a root in a bracketing interval.
- *
- * <p> When calling this method one of the following must be true. Either ga == 0, gb
- * == 0, (ga < 0 and gb > 0), or (ga > 0 and gb < 0).
- *
- * @param interpolator that covers the interval.
- * @param ta earliest possible time for root.
- * @param ga g(ta).
- * @param tb latest possible time for root.
- * @param gb g(tb).
- * @return if a zero crossing was found.
- */
- private boolean findRoot(final OrekitStepInterpolator interpolator,
- final AbsoluteDate ta, final double ga,
- final AbsoluteDate tb, final double gb) {
- // check there appears to be a root in [ta, tb]
- check(ga == 0.0 || gb == 0.0 || ga > 0.0 && gb < 0.0 || ga < 0.0 && gb > 0.0);
- final double convergence = detector.getThreshold();
- final int maxIterationCount = detector.getMaxIterationCount();
- final BracketedUnivariateSolver<UnivariateFunction> solver =
- new BracketingNthOrderBrentSolver(0, convergence, 0, 5);
- // prepare loop below
- AbsoluteDate loopT = ta;
- double loopG = ga;
- // event time, just at or before the actual root.
- AbsoluteDate beforeRootT = null;
- double beforeRootG = Double.NaN;
- // time on the other side of the root.
- // Initialized the the loop below executes once.
- AbsoluteDate afterRootT = ta;
- double afterRootG = 0.0;
- // check for some conditions that the root finders don't like
- // these conditions cannot not happen in the loop below
- // the ga == 0.0 case is handled by the loop below
- if (ta.equals(tb)) {
- // both non-zero but times are the same. Probably due to reset state
- beforeRootT = ta;
- beforeRootG = ga;
- afterRootT = shiftedBy(beforeRootT, convergence);
- afterRootG = g(interpolator.getInterpolatedState(afterRootT));
- } else if (ga != 0.0 && gb == 0.0) {
- // hard: ga != 0.0 and gb == 0.0
- // look past gb by up to convergence to find next sign
- // throw an exception if g(t) = 0.0 in [tb, tb + convergence]
- beforeRootT = tb;
- beforeRootG = gb;
- afterRootT = shiftedBy(beforeRootT, convergence);
- afterRootG = g(interpolator.getInterpolatedState(afterRootT));
- } else if (ga != 0.0) {
- final double newGa = g(interpolator.getInterpolatedState(ta));
- if (ga > 0 != newGa > 0) {
- // both non-zero, step sign change at ta, possibly due to reset state
- final AbsoluteDate nextT = minTime(shiftedBy(ta, convergence), tb);
- final double nextG = g(interpolator.getInterpolatedState(nextT));
- if (nextG > 0.0 == g0Positive) {
- // the sign change between ga and newGa just moved the root less than one convergence
- // threshold later, we are still in a regular search for another root before tb,
- // we just need to fix the bracketing interval
- // (see issue https://github.com/Hipparchus-Math/hipparchus/issues/184)
- loopT = nextT;
- loopG = nextG;
- } else {
- beforeRootT = ta;
- beforeRootG = newGa;
- afterRootT = nextT;
- afterRootG = nextG;
- }
- }
- }
- // loop to skip through "fake" roots, i.e. where g(t) = g'(t) = 0.0
- // executed once if we didn't hit a special case above
- while ((afterRootG == 0.0 || afterRootG > 0.0 == g0Positive) &&
- strictlyAfter(afterRootT, tb)) {
- if (loopG == 0.0) {
- // ga == 0.0 and gb may or may not be 0.0
- // handle the root at ta first
- beforeRootT = loopT;
- beforeRootG = loopG;
- afterRootT = minTime(shiftedBy(beforeRootT, convergence), tb);
- afterRootG = g(interpolator.getInterpolatedState(afterRootT));
- } else {
- // both non-zero, the usual case, use a root finder.
- // time zero for evaluating the function f. Needs to be final
- final AbsoluteDate fT0 = loopT;
- final double tbDouble = tb.durationFrom(fT0);
- final double middle = 0.5 * tbDouble;
- final UnivariateFunction f = dt -> {
- // use either fT0 or tb as the base time for shifts
- // in order to ensure we reproduce exactly those times
- // using only one reference time like fT0 would imply
- // to use ft0.shiftedBy(tbDouble), which may be different
- // from tb due to numerical noise (see issue 921)
- final AbsoluteDate t;
- if (forward == dt <= middle) {
- // use start of interval as reference
- t = fT0.shiftedBy(dt);
- } else {
- // use end of interval as reference
- t = tb.shiftedBy(dt - tbDouble);
- }
- return g(interpolator.getInterpolatedState(t));
- };
- // tb as a double for use in f
- if (forward) {
- try {
- final Interval interval =
- solver.solveInterval(maxIterationCount, f, 0, tbDouble);
- beforeRootT = fT0.shiftedBy(interval.getLeftAbscissa());
- beforeRootG = interval.getLeftValue();
- afterRootT = fT0.shiftedBy(interval.getRightAbscissa());
- afterRootG = interval.getRightValue();
- // CHECKSTYLE: stop IllegalCatch check
- } catch (RuntimeException e) {
- // CHECKSTYLE: resume IllegalCatch check
- throw new OrekitException(e, OrekitMessages.FIND_ROOT,
- detector, loopT, loopG, tb, gb, lastT, lastG);
- }
- } else {
- try {
- final Interval interval =
- solver.solveInterval(maxIterationCount, f, tbDouble, 0);
- beforeRootT = fT0.shiftedBy(interval.getRightAbscissa());
- beforeRootG = interval.getRightValue();
- afterRootT = fT0.shiftedBy(interval.getLeftAbscissa());
- afterRootG = interval.getLeftValue();
- // CHECKSTYLE: stop IllegalCatch check
- } catch (RuntimeException e) {
- // CHECKSTYLE: resume IllegalCatch check
- throw new OrekitException(e, OrekitMessages.FIND_ROOT,
- detector, tb, gb, loopT, loopG, lastT, lastG);
- }
- }
- }
- // tolerance is set to less than 1 ulp
- // assume tolerance is 1 ulp
- if (beforeRootT.equals(afterRootT)) {
- afterRootT = nextAfter(afterRootT);
- afterRootG = g(interpolator.getInterpolatedState(afterRootT));
- }
- // check loop is making some progress
- check(forward && afterRootT.compareTo(beforeRootT) > 0 ||
- !forward && afterRootT.compareTo(beforeRootT) < 0);
- // setup next iteration
- loopT = afterRootT;
- loopG = afterRootG;
- }
- // figure out the result of root finding, and return accordingly
- if (afterRootG == 0.0 || afterRootG > 0.0 == g0Positive) {
- // loop gave up and didn't find any crossing within this step
- return false;
- } else {
- // real crossing
- check(beforeRootT != null && !Double.isNaN(beforeRootG));
- // variation direction, with respect to the integration direction
- increasing = !g0Positive;
- pendingEventTime = beforeRootT;
- stopTime = beforeRootG == 0.0 ? beforeRootT : afterRootT;
- pendingEvent = true;
- afterEvent = afterRootT;
- afterG = afterRootG;
- // check increasing set correctly
- check(afterG > 0 == increasing);
- check(increasing == gb >= ga);
- return true;
- }
- }
- /**
- * Get the next number after the given number in the current propagation direction.
- *
- * @param t input time
- * @return t +/- 1 ulp depending on the direction.
- */
- private AbsoluteDate nextAfter(final AbsoluteDate t) {
- return t.shiftedBy(forward ? +Precision.EPSILON : -Precision.EPSILON);
- }
- /** Get the occurrence time of the event triggered in the current
- * step.
- * @return occurrence time of the event triggered in the current
- * step.
- */
- public AbsoluteDate getEventDate() {
- return pendingEventTime;
- }
- /**
- * Try to accept the current history up to the given time.
- *
- * <p> It is not necessary to call this method before calling {@link
- * #doEvent(SpacecraftState)} with the same state. It is necessary to call this
- * method before you call {@link #doEvent(SpacecraftState)} on some other event
- * detector.
- *
- * @param state to try to accept.
- * @param interpolator to use to find the new root, if any.
- * @return if the event detector has an event it has not detected before that is on or
- * before the same time as {@code state}. In other words {@code false} means continue
- * on while {@code true} means stop and handle my event first.
- */
- public boolean tryAdvance(final SpacecraftState state,
- final OrekitStepInterpolator interpolator) {
- final AbsoluteDate t = state.getDate();
- // check this is only called before a pending event.
- check(!pendingEvent || !strictlyAfter(pendingEventTime, t));
- final boolean meFirst;
- if (strictlyAfter(t, earliestTimeConsidered)) {
- // just found an event and we know the next time we want to search again
- meFirst = false;
- } else {
- // check g function to see if there is a new event
- final double g = g(state);
- final boolean positive = g > 0;
- if (positive == g0Positive) {
- // g function has expected sign
- g0 = g; // g0Positive is the same
- meFirst = false;
- } else {
- // found a root we didn't expect -> find precise location
- final AbsoluteDate oldPendingEventTime = pendingEventTime;
- final boolean foundRoot = findRoot(interpolator, t0, g0, t, g);
- // make sure the new root is not the same as the old root, if one exists
- meFirst = foundRoot && !pendingEventTime.equals(oldPendingEventTime);
- }
- }
- if (!meFirst) {
- // advance t0 to the current time so we can't find events that occur before t
- t0 = t;
- }
- return meFirst;
- }
- /**
- * Notify the user's listener of the event. The event occurs wholly within this method
- * call including a call to {@link EventDetector#resetState(SpacecraftState)}
- * if necessary.
- *
- * @param state the state at the time of the event. This must be at the same time as
- * the current value of {@link #getEventDate()}.
- * @return the user's requested action and the new state if the action is {@link
- * Action#RESET_STATE Action.RESET_STATE}.
- * Otherwise the new state is {@code state}. The stop time indicates what time propagation
- * should stop if the action is {@link Action#STOP Action.STOP}.
- * This guarantees the integration will stop on or after the root, so that integration
- * may be restarted safely.
- */
- public EventOccurrence doEvent(final SpacecraftState state) {
- // check event is pending and is at the same time
- check(pendingEvent);
- check(state.getDate().equals(this.pendingEventTime));
- final Action action = detector.eventOccurred(state, increasing == forward);
- final SpacecraftState newState;
- if (action == Action.RESET_STATE) {
- newState = detector.resetState(state);
- } else {
- newState = state;
- }
- // clear pending event
- pendingEvent = false;
- pendingEventTime = null;
- // setup for next search
- earliestTimeConsidered = afterEvent;
- t0 = afterEvent;
- g0 = afterG;
- g0Positive = increasing;
- // check g0Positive set correctly
- check(g0 == 0.0 || g0Positive == g0 > 0);
- return new EventOccurrence(action, newState, stopTime);
- }
- /**
- * Shift a time value along the current integration direction: {@link #forward}.
- *
- * @param t the time to shift.
- * @param delta the amount to shift.
- * @return t + delta if forward, else t - delta. If the result has to be rounded it
- * will be rounded to be before the true value of t + delta.
- */
- private AbsoluteDate shiftedBy(final AbsoluteDate t, final double delta) {
- if (forward) {
- final AbsoluteDate ret = t.shiftedBy(delta);
- if (ret.durationFrom(t) > delta) {
- return ret.shiftedBy(-Precision.EPSILON);
- } else {
- return ret;
- }
- } else {
- final AbsoluteDate ret = t.shiftedBy(-delta);
- if (t.durationFrom(ret) > delta) {
- return ret.shiftedBy(+Precision.EPSILON);
- } else {
- return ret;
- }
- }
- }
- /**
- * Get the time that happens first along the current propagation direction: {@link
- * #forward}.
- *
- * @param a first time
- * @param b second time
- * @return min(a, b) if forward, else max (a, b)
- */
- private AbsoluteDate minTime(final AbsoluteDate a, final AbsoluteDate b) {
- return (forward ^ (a.compareTo(b) > 0)) ? a : b;
- }
- /**
- * Check the ordering of two times.
- *
- * @param t1 the first time.
- * @param t2 the second time.
- * @return true if {@code t2} is strictly after {@code t1} in the propagation
- * direction.
- */
- private boolean strictlyAfter(final AbsoluteDate t1, final AbsoluteDate t2) {
- if (t1 == null || t2 == null) {
- return false;
- } else {
- return forward ? t1.compareTo(t2) < 0 : t2.compareTo(t1) < 0;
- }
- }
- /**
- * Same as keyword assert, but throw a {@link MathRuntimeException}.
- *
- * @param condition to check
- * @throws MathRuntimeException if {@code condition} is false.
- */
- private void check(final boolean condition) throws MathRuntimeException {
- if (!condition) {
- throw new OrekitInternalError(null);
- }
- }
- /**
- * Class to hold the data related to an event occurrence that is needed to decide how
- * to modify integration.
- */
- public static class EventOccurrence {
- /** User requested action. */
- private final Action action;
- /** New state for a reset action. */
- private final SpacecraftState newState;
- /** The time to stop propagation if the action is a stop event. */
- private final AbsoluteDate stopDate;
- /**
- * Create a new occurrence of an event.
- *
- * @param action the user requested action.
- * @param newState for a reset event. Should be the current state unless the
- * action is {@link Action#RESET_STATE}.
- * @param stopDate to stop propagation if the action is {@link Action#STOP}. Used
- * to move the stop time to just after the root.
- */
- EventOccurrence(final Action action,
- final SpacecraftState newState,
- final AbsoluteDate stopDate) {
- this.action = action;
- this.newState = newState;
- this.stopDate = stopDate;
- }
- /**
- * Get the user requested action.
- *
- * @return the action.
- */
- public Action getAction() {
- return action;
- }
- /**
- * Get the new state for a reset action.
- *
- * @return the new state.
- */
- public SpacecraftState getNewState() {
- return newState;
- }
- /**
- * Get the new time for a stop action.
- *
- * @return when to stop propagation.
- */
- public AbsoluteDate getStopDate() {
- return stopDate;
- }
- }
- }