Move non-event orbit integrations onto the fortnum ODE solver#46
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krystophny wants to merge 8 commits into
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Move non-event orbit integrations onto the fortnum ODE solver#46krystophny wants to merge 8 commits into
krystophny wants to merge 8 commits into
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Wire the fortnum numerical-core library via CMake FetchContent (git@github.com:lazy-fortran/fortnum.git, pinned to a7faa3c) guarded by if(NOT TARGET fortnum) so a parent build that already provides the target is reused. Link the static library into neo_rt; its module directory is exported PUBLIC, so neo_rt and the diagnostics library that links neo_rt both see the fortnum modules. This commit adds the dependency without changing any solver call site; the existing DVODE path is untouched and still in use. Subsequent commits move the orbit integrations onto the fortnum ODE solver and then drop DVODE.
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Replace the DVODE calls in the two fixed-interval, no-event integrations with the fortnum DOP853 solver: - orbit.f90 bounce_fast: ode_solve_dop from 0 to taub, take the final recorded state. The fortnum status maps onto the legacy istate the transport caller branches on (2 success, -1 step budget exhausted, 0 other), so dvode_error_context still fires on the exhausted-budget case and the public bounce_fast signature is unchanged. - diag/diag_bounce_debug.f90 probe_bounce: ode_integrate_dop, then read solution%nsteps, solution%nrejected and the last solution%h into the diagnostic columns the scan previously filled from get_stats. - freq.f90: drop the vode_thread_init shim. The fortnum integrator keeps no module-level state, so freq_thread_init has nothing VODE-specific to initialise. The event-based bounce_integral and the vode dependency itself stay until the next commit so this change is reviewable on its own.
Two defects surfaced once bounce_fast ran on fortnum DOP853 instead of DVODE, both caught only by the CI Debug build (gfortran 13, -ffpe-trap=zero,overflow,invalid,underflow): - timestep_transport left ydot(7), the unused abs(B) slot, uninitialised. DVODE ignored the stray derivative, but DOP853 carries every component through its stage combinations, so the leftover denormal tripped the underflow trap inside dop853_step. Zero the trailing integrands the routine does not compute, matching what timestep already does. - The bounceavg(3:4) perturbed-Hamiltonian integrands oscillate at the resonant harmonic but are driven, not fed back into the orbit, so the rtol error estimate barely constrains them. The unconstrained adaptive step grew too coarse and the oscillatory integral came out wrong (D11 off by an order of magnitude). Drive bounce_fast through ode_integrate_dop with hmax = taub/200 to keep the step fine enough; this recovers the DVODE result to four significant figures.
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This was referenced Jun 14, 2026
Replace the DOP853 substitution in bounce_fast with fortnum vode (DVODE MF=10 nonstiff Adams), relative tolerance 1e-9 and a per-component absolute tolerance 1e-10 (DVODE ITOL=2), over the single bounce span. This restores the variable-order method NEO-RT drove through DVODE before the migration, so the oscillatory bounce-average integrands no longer need the artificial DOP853 step cap. Re-pin fortnum to the commit that adds the two-event root support the bounce_integral event path needs.
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Move the non-event orbit integrations (
bounce_fast) from DVODE_F90 onto thefortnum nonstiff variable-order Adams integrator (
fortnum_ode_vode, DVODEMF=10 equivalent): single span
[0, taub], scalar relerr 1e-9, per-componentabserr 1e-10 (ITOL=2). Re-pins the fortnum dependency from v0.1.0 to fortnum
main 974dcf1.
Call sites
src/orbit.f90bounce_fast: replaces thedvode_f90MF=10 call withvode_init+vode_integrate_toover the single bounce span; maps thefortnum status onto the legacy
istateconvention (2 success, -1 stepbudget, 0 failure).
CMakeLists.txt:FetchContentGIT_TAG->974dcf12e2599ffa5882380207d753c8e8e0a9f6.Verification
Golden record
test/golden_record/test_golden_record.pyagainst theDVODE_F90-generated
golden.h5(bar rtol=1e-8, atol=1e-15), CONFIG=Fast,worst relative deviation per output:
The
bounce_fastpath on fortnum vode agrees with the DVODE reference farbetter than the prior DOP853 substitution (which was ~1e-4 to ~15% on
output):magfiematches exactly (rel 0). The bounce-averagedoutput(D11/D12)agrees to 1e-9..3.5e-7.
The golden test still reports 9 failed on this branch, for two reasons:
integral/torque_integralfailures (rel ~1e-4) come fromthe event-path
bounce_integral, which on this branch still uses theDOP853 chunked scan; its taub is not the DVODE root. That path is migrated
in the stacked PR Move bounce_integral event search onto fortnum and drop vode #47.
bounce_fastagreement tops out at ~3.6e-7 (worst case 0p600),above the 1e-8 bar. fortnum vode matches DVODE_F90 to about its requested
tolerance, not bit-for-bit (the fortnum suite asserts accuracy versus the
analytic solution, not bit-identity with DVODE_F90), so the
DVODE-generated golden cannot be reproduced at rtol=1e-8.
The golden record is regenerated and RK4-validated in the stacked #47, where the event-path
bounce_integralmoves onto fortnum and its taub stops latching onto multiple-period bounce returns at the near-separatrix trapped spline nodes (seetest/golden_record/REGENERATION.md). This branch keeps the DVODE/DOP853 event path, so the regenerated golden lands with #47, not here. Thebounce_fastchange on this branch shifts only the bounce-averaged Om_tB/D11/D12 at the ~1e-7 level; an independent 2e6-substep RK4 of the orbit ODE confirms the fortnum Om_tB bounce average to <1e-6 across the trapped grid. No tolerances were weakened.Note: fortnum pin updated to current main (92de6e9) after a fortnum history rewrite; old shas no longer resolve.