Add callback/event support for operator splitting integrator (Fixes #36) #46
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This implements callback support for OperatorSplittingIntegrator, addressing issue SciML#36. Key changes: - Add savevalues! function to save solution values during callback execution - Add handle_callbacks! function to process callbacks after each step - Add apply_discrete_callback! for full discrete callback support - Add apply_continuous_callback_simple! for simplified continuous callbacks (endpoint-only checking without full root-finding) - Modify __step! to call handle_callbacks! after advancing the solution - Implement proper u_modified! to track when callbacks modify the solution - Add comprehensive test suite for callback functionality Design decisions: - Callbacks are handled at the outer integrator level only, after all subproblems are solved for a timestep. This ensures callbacks have access to the full solution state. - Continuous callbacks use simplified endpoint checking rather than full root-finding, as root-finding across split subproblems is not well-defined for operator splitting methods. - When u is modified by a callback, it is propagated to uprev so the next step starts correctly. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <[email protected]>
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Summary
This PR implements callback and event support for
OperatorSplittingIntegrator, addressing issue #36.u_modified!tracking for solution modificationssavevalues!function for callback-triggered savesDesign Decisions
As discussed in issue #36, there are two main challenges for callbacks in operator splitting:
Which integrator triggers which callback: We handle callbacks ONLY at the outer integrator level, AFTER all subproblems are solved for a timestep. This ensures callbacks have access to the full solution state.
Visibility of unknowns: By processing callbacks at the outer integrator level, callbacks can see the full solution
u, not just partial views that individual subintegrators work with.For continuous callbacks, full root-finding across split subproblems is not well-defined, so we use simplified endpoint checking (detect sign changes between
tprevandt). Users requiring precise event timing should use smaller timesteps or ensure their callback conditions align with the timestep boundaries.Test plan
u- modification propagates correctlysave_positions- saves work correctlyu_modified!functionality - flag is properly set/clearedAll tests pass locally.
cc @ChrisRackauckas
🤖 Generated with Claude Code