Re-apply: Widen UJacobianWrapper.p for nested ForwardDiff through Rosenbrock (#3381)#3587
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…ciML#3381) Re-applies the changes from PR SciML#3414 on top of current master. The original PR was reverted by SciML#3586; this restores it now that SciML#3488 (JacReuseState dtgamma fix) has landed and the two changes coexist without conflict (they touch disjoint files). Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Move the nested-Dual `p` widening from per-`jacobian!`-call to once at cache build time. The inner Dual eltype is fixed once `JacobianConfig` is built, so the widened `uf` can be cached in the Rosenbrock cache struct directly. `jacobian!` still calls `_widen_uf_p_for_jac`, but the fast-path (`Tp === inner_T && return f`) returns the cached `uf` unchanged with zero allocations. Measured on the issue SciML#3381 nested-Dual MWE: - Before: 240 bytes/jacobian! call (one Vector{nested_dual} convert + one UJacobianWrapper struct rebuild via `@set f.p`). - After: 0 bytes/jacobian! call. Non-nested case is unchanged (already 0 bytes/call via the `Tp <: ForwardDiff.Dual || return f` fast-path). Patches all four IIP cache builders in `rosenbrock_caches.jl`: Rosenbrock23, Rosenbrock32, RodasTableauAlgorithms, HybridExplicitImplicitRK. Other algorithms (BDF, SDIRK, FIRK, …) keep the per-call widen for now; the same pattern can be lifted into their caches as a follow-up. Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Asserts the cache-time pre-widen invariant from the previous commit: - `eltype(integ.cache.uf.p)` must equal the inner nested-Dual eltype. - `_widen_uf_p_for_jac` on the cached uf must allocate zero bytes (fast-path returns `f` unchanged). Catches regressions in either direction: a missing pre-widen line in a cache builder fails the eltype check; a broken fast-path in the helper fails the @allocated check. Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
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Reopens the fix from #3414, which was reverted by #3586. Rebased onto current master.
Why now
Per @ChrisRackauckas's comment on #3381 (2026-04-30), this is the intended fix for the tag-ordering issue (
UJacobianWrapper.pcarrying the outerNonlinearSolveTagDuals while the inner Rosenbrock FD needs to wrap them again). #3488 has since merged and fixes a different nested-FD path (JacReuseStatedtgamma storage, #3486) — the two changes touch disjoint files and coexist cleanly.Diff vs. master
Same as the original #3414 — 4 files, 157 insertions / 11 deletions. The revert in #3586 only touched these 4 files; reverting that revert produced no conflicts against #3488's changes (
derivative_utils.jl,rosenbrock_caches.jl).lib/DiffEqBase/ext/DiffEqBaseForwardDiffExt.jllib/OrdinaryDiffEqDifferentiation/src/derivative_wrappers.jllib/OrdinaryDiffEqDifferentiation/test/nested_forwarddiff_tests.jl(new)lib/OrdinaryDiffEqDifferentiation/test/runtests.jlTest plan
FirstAutodiffJacError.🤖 Generated with Claude Code