Fix PresetTimeCallback being skipped with certain constant lags#368
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When constant lags like [0.2, 4] are used, propagated tstops accumulate floating-point error through repeated t + lag additions. After 45 steps of lag 0.2, the propagated tstop for t=9.0 becomes 8.999999999999996. The handle_discontinuities! function was removing all tstops within 10eps(t) of the current time, including user-specified tstops from PresetTimeCallback. This caused callbacks to be silently skipped when a propagated tstop happened to land within eps of the callback time. The fix restricts the tstop cleanup to only remove from tstops_propagated, never from opts.tstops. User-specified tstops should never be removed by discontinuity handling. Fixes SciML/DifferentialEquations.jl#1124 Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
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Summary
PresetTimeCallbackwas silently skipped when constant lag multiples coincided with preset callback times due to floating-point accumulation errorRoot Cause
When constant lags like
[0.2, 4]are used, propagated tstops accumulate floating-point error through repeatedt + lagadditions. After 45 steps of lag 0.2, the propagated tstop for t=9.0 becomes8.999999999999996.The
handle_discontinuities!function was removing all tstops within10eps(t)of the current time from bothopts.tstops(user callbacks) andtstops_propagated(lag-generated stops). When the propagated tstop landed just below 9.0, and integrator.t was snapped to that value, the user's 9.0 tstop was within the epsilon tolerance and got erroneously removed.The Fix
The fix restricts the tstop cleanup in
handle_discontinuities!to only remove fromtstops_propagated, never fromopts.tstops. User-specified tstops (fromPresetTimeCallback, etc.) should never be removed by discontinuity handling.Test Plan
Fixes SciML/DifferentialEquations.jl#1124
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