Add tolerance in DetectorBasedEventState check

Hipparchus development
1

Hi everyone,

I encounter a bug using AbstractIntegrator and DetectorBasedEventState in Hipparchus 4.0.1.

  • Inside AbstractIntegrator, the state is retrieved at detected date using an interpolator of ClassicalRungeKuttaStateInterpolator. As the first screenshot shows, the event date is 17016.237999999998 not rounded whereas after the interpolation, the eventState.time is truncated to 17016.238.
  • After that, the event is validated by the method doEvent of the DetectorBasedEventState, where a check of time’s equality is made (screenshot 3). This is where the snake bites its tail, as the interpolated state time is truncated and not the detected event time and the exception is raised.
  • When I look at how it is interpolated, it appears that the state is returned as it is when the time difference is lower than the least significant bit, LSB (screenshot 2).

The most straight-forward solution I think of, is to add the same tolerance of LSB, during the check, instead of the equality.
The deep correction would be to have the detection giving the right time but I suppose it is harder as the LSB is expected.

Can the first correction be foreseen ?

Thanks a lot !

Clement

Screenshot 1
Screenshot 11920×810 84 KB

2

screenshot 2
screenshot 21463×691 64.8 KB

3

pourOrekit2
pourOrekit21390×453 44.9 KB

(For some reason, since I’m a new user, I’m not allowed to upload more than one figure, so I just put in the comment section. Sorry for that)

4

Could you post a failing test case? Then we can add it to CloseEventsTest.

5

Hi @evan.ward and @clementyng

I reproduced the problem in an Orekit context. It shall be noted that in this case the propagation end epoch is equal to the maneuver thrust end. I thinks that’s an intersting starting point for investigation.

    @Test
    void testBugRk4() {
        GravityFieldFactory.addPotentialCoefficientsReader(new GRGSFormatReader("grim4s4_gr", true));
        UTCScale utc = TimeScalesFactory.getUTC();
        // Initialize spacecraft
        final CartesianOrbit cartesian = new CartesianOrbit(new PVCoordinates(new Vector3D(1897711.783316963, 4938498.102677712, -4414426.470208112),
                                                                              new Vector3D(-525.3256319053179, -4937.568767036118, -5754.938592063509)),
                                                            FramesFactory.getTOD(false),
                                                            new AbsoluteDate(2025, 6, 25, 14, 30, 32.965, utc),
                                                            Constants.WGS84_EARTH_MU);
        final double mass = 300.0;

        // Initialize propagator
        final NumericalPropagator numerical = new NumericalPropagator(new ClassicalRungeKuttaIntegrator(60.0));
        numerical.addForceModel(new HolmesFeatherstoneAttractionModel(FramesFactory.getITRF(IERSConventions.IERS_2010, false),
                                                                      GravityFieldFactory.getNormalizedProvider(10, 10)));
        numerical.addForceModel(new Maneuver(null,
                                             new DateBasedManeuverTriggers(new AbsoluteDate(2025, 6, 25, 14, 54, 53.247, utc),
                                                                           720.0),
                                             new BasicConstantThrustPropulsionModel(0.015, 1161, Vector3D.PLUS_I, "Cucchiethurst")));
        numerical.setInitialState(new SpacecraftState(cartesian).withMass(mass));

        // Propagate
        numerical.propagate(new AbsoluteDate(2025, 6, 25, 10, 23, 17.009, utc), new AbsoluteDate(2025, 6, 25, 15, 6, 53.247, utc));
    }

The stacktrace is:

Caused by: org.hipparchus.exception.MathRuntimeException: internal error, please fill a bug report at ``https://github.com/Hipparchus-Math/hipparchus/issues
at org.hipparchus.exception.MathRuntimeException.createInternalError(MathRuntimeException.java:69)
at org.hipparchus.ode.events.DetectorBasedEventState.check(DetectorBasedEventState.java:585)
at org.hipparchus.ode.events.DetectorBasedEventState.doEvent(DetectorBasedEventState.java:505)
at org.hipparchus.ode.AbstractIntegrator.acceptStep(AbstractIntegrator.java:369)
at org.hipparchus.ode.nonstiff.FixedStepRungeKuttaIntegrator.integrate(FixedStepRungeKuttaIntegrator.java:168)

An interesting observation is that using a Dormand-Prince integrator, there is no issue.

Thank you,
Bryan

6

Additionaly, I did this small test on epochs

      // Epochs
        final AbsoluteDate maneuverStart = new AbsoluteDate(2025, 6, 25, 14, 54, 53.247, utc);
        final AbsoluteDate maneuverEnd = maneuverStart.shiftedBy(720.0);
        final AbsoluteDate propagationStart = new AbsoluteDate(2025, 6, 25, 10, 23, 17.009, utc);
        final AbsoluteDate propagationEnd = new AbsoluteDate(2025, 6, 25, 15, 6, 53.247, utc);

        // Print some delta time
        System.out.println(propagationEnd.toString(utc));
        System.out.println(maneuverEnd.toString(utc));
        System.out.println(propagationEnd.durationFrom(maneuverEnd));
        System.out.println(propagationEnd.durationFrom(propagationStart));
        System.out.println(maneuverEnd.durationFrom(propagationStart));

The obtained results are

2025-06-25T15:06:53.246999999999999872
2025-06-25T15:06:53.246999999999999872
0.0
17016.238
17016.238