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Return u-field tangent for structural VectorOfArray cotangents - #656
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ChrisRackauckas merged 1 commit intoSep 22, 2026
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Zygote's `literal_getproperty` adjoint for `A.u` received per-element cotangents and always rebuilt a VectorOfArray/DiffEqArray from them. When the elements are structural tangents — e.g. the per-solution NamedTuples produced when differentiating `ensemble_sol.u` — the VectorOfArray constructor fails on `ndims(::NamedTuple)`, breaking ensemble differentiation (SciML/DifferentialEquations.jl#1149). Detect non-numeric structural elements (anything that is not nothing, an AbstractZero, an AbstractArray or a Number) and return the `u`-field tangent `(; u = collect(d))` instead. Numeric cotangents keep the existing VectorOfArray/DiffEqArray behavior. Generated with [Devin](https://devin.ai) Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com> Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com> Agent-Harness: Devin CLI 3000.10.31 Agent-Model: SWE-2 Max Agent-Session: local transcript /home/crackauc/.local/share/devin/cli/summaries/history_d4203d25c3424828.md
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Ships #656: the u-field tangent is returned for structural VectorOfArray cotangents. Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com> Co-Authored-By: Claude <noreply@anthropic.com> Agent-Harness: Claude Code 2.1.273 Agent-Model: claude-opus-5[1m] Agent-Session: 6a01e420-3436-4518-83cc-6cd853283cfb (local transcript; this harness publishes no conversation URL)
ChrisRackauckas
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Sep 23, 2026
Ships #656: the u-field tangent is returned for structural VectorOfArray cotangents. Agent-Harness: Claude Code 2.1.273 Agent-Model: claude-opus-5[1m] Agent-Session: 6a01e420-3436-4518-83cc-6cd853283cfb (local transcript; this harness publishes no conversation URL) Co-authored-by: Claude <noreply@anthropic.com>
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Summary
Zygote's
literal_getpropertyadjoint forA.u(vofa_u_adjoint) received per-element cotangents and always rebuilt aVectorOfArray/DiffEqArrayfrom them. When the elements are structural tangents — e.g. the per-solutionNamedTuples produced when differentiatingensemble_sol.ufor anEnsembleSolution— theVectorOfArrayconstructor fails onndims(::NamedTuple), breaking ensemble differentiation (SciML/DifferentialEquations.jl#1149, where Zygote threwMethodErrorfromVectorOfArray(vec::Vector{Any})while ForwardDiff computed the gradient correctly).vofa_u_adjointnow detects non-numeric structural elements (anything that is notnothing, anAbstractZero, anAbstractArrayor aNumber) and returns theu-field tangent(; u = collect(d))instead. Numeric cotangents keep the existingVectorOfArray/DiffEqArraybehavior; mixed vectors withnothing/AbstractZeroholes still hit the numeric path as before.Test plan
test/AD/adjoints.jl:vofa_u_adjointonAny[(; u = ..., t = ...), nothing, (; ...)]for bothVectorOfArrayandDiffEqArraymust return aNamedTuplewith the expected.u.Fails before the fix (revert this patch and run
test/AD/adjoints.jl):Passes after:
julia --project=test/AD test/AD/adjoints.jlexits 0 (all@tests silent on success).sol.t[end]gradient in SciMLSensitivity (companion PR) matches ForwardDiff to ~1e-5 under bothEnsembleSerialandEnsembleThreads.🤖 Generated with Devin (harness: Devin CLI 3000.10.31, model: SWE-2 Max, session: local transcript /home/crackauc/.local/share/devin/cli/summaries/history_d4203d25c3424828.md)