Examples with FieldOrekitStepInterpolator org.orekit.propagation.sampling.FieldOrekitStepInterpolator used on opensource projects

Example 1 with FieldOrekitStepInterpolator

use of org.orekit.propagation.sampling.FieldOrekitStepInterpolator in project Orekit by CS-SI.

the class FieldEventState method findRoot.

/**
 * 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.
 * @throws OrekitException if the event detector throws one
 */
private boolean findRoot(final FieldOrekitStepInterpolator<T> interpolator, final FieldAbsoluteDate<T> ta, final T ga, final FieldAbsoluteDate<T> tb, final T gb) throws OrekitException {
    final T zero = ga.getField().getZero();
    // check there appears to be a root in [ta, tb]
    check(ga.getReal() == 0.0 || gb.getReal() == 0.0 || (ga.getReal() > 0.0 && gb.getReal() < 0.0) || (ga.getReal() < 0.0 && gb.getReal() > 0.0));
    final T convergence = detector.getThreshold();
    final int maxIterationCount = detector.getMaxIterationCount();
    final BracketedUnivariateSolver<UnivariateFunction> solver = new BracketingNthOrderBrentSolver(0, convergence.getReal(), 0, 5);
    // event time, just at or before the actual root.
    FieldAbsoluteDate<T> beforeRootT = null;
    T beforeRootG = zero.add(Double.NaN);
    // time on the other side of the root.
    // Initialized the the loop below executes once.
    FieldAbsoluteDate<T> afterRootT = ta;
    T afterRootG = zero;
    // 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.getReal() != 0.0 && gb.getReal() == 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.getReal() != 0.0) {
        final T newGa = g(interpolator.getInterpolatedState(ta));
        if (ga.getReal() > 0 != newGa.getReal() > 0) {
            // both non-zero, step sign change at ta, possibly due to reset state
            beforeRootT = ta;
            beforeRootG = newGa;
            afterRootT = minTime(shiftedBy(beforeRootT, convergence), tb);
            afterRootG = g(interpolator.getInterpolatedState(afterRootT));
        }
    }
    // 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
    FieldAbsoluteDate<T> loopT = ta;
    T loopG = ga;
    while ((afterRootG.getReal() == 0.0 || afterRootG.getReal() > 0.0 == g0Positive) && strictlyAfter(afterRootT, tb)) {
        if (loopG.getReal() == 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.
            try {
                // time zero for evaluating the function f. Needs to be final
                final FieldAbsoluteDate<T> fT0 = loopT;
                final UnivariateFunction f = dt -> {
                    try {
                        return g(interpolator.getInterpolatedState(fT0.shiftedBy(dt))).getReal();
                    } catch (OrekitException oe) {
                        throw new OrekitExceptionWrapper(oe);
                    }
                };
                // tb as a double for use in f
                final T tbDouble = tb.durationFrom(fT0);
                if (forward) {
                    final Interval interval = solver.solveInterval(maxIterationCount, f, 0, tbDouble.getReal());
                    beforeRootT = fT0.shiftedBy(interval.getLeftAbscissa());
                    beforeRootG = zero.add(interval.getLeftValue());
                    afterRootT = fT0.shiftedBy(interval.getRightAbscissa());
                    afterRootG = zero.add(interval.getRightValue());
                } else {
                    final Interval interval = solver.solveInterval(maxIterationCount, f, tbDouble.getReal(), 0);
                    beforeRootT = fT0.shiftedBy(interval.getRightAbscissa());
                    beforeRootG = zero.add(interval.getRightValue());
                    afterRootT = fT0.shiftedBy(interval.getLeftAbscissa());
                    afterRootG = zero.add(interval.getLeftValue());
                }
            } catch (OrekitExceptionWrapper oew) {
                throw oew.getException();
            }
        }
        // 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.getReal() == 0.0 || afterRootG.getReal() > 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.getReal()));
        // variation direction, with respect to the integration direction
        increasing = !g0Positive;
        pendingEventTime = beforeRootT;
        stopTime = beforeRootG.getReal() == 0.0 ? beforeRootT : afterRootT;
        pendingEvent = true;
        afterEvent = afterRootT;
        afterG = afterRootG;
        // check increasing set correctly
        check(afterG.getReal() > 0 == increasing);
        check(increasing == gb.getReal() >= ga.getReal());
        return true;
    }
}