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Return u-field tangent for structural VectorOfArray cotangents #656

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Merged
ChrisRackauckas merged 1 commit into from
Sep 22, 2026
Merged

Return u-field tangent for structural VectorOfArray cotangents #656

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7 changes: 7 additions & 0 deletions ext/RecursiveArrayToolsZygoteExt.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -90,6 +90,11 @@ Zygote.@adjoint function Zygote.literal_getproperty(A::RecursiveArrayTools.Abstr
end

function vofa_u_adjoint(d, A::RecursiveArrayTools.AbstractVectorOfArray)
# Structural tangents (e.g. per-solution NamedTuples for an
# EnsembleSolution's `u`) cannot be stored in a VectorOfArray, so the
# cotangent of `A` is the `u`-field tangent itself.
all(d_i -> isnothing(d_i) || d_i isa Union{AbstractZero, AbstractArray, Number}, d) ||
return (; u = collect(d))
m = map(enumerate(d)) do (idx, d_i)
(isnothing(d_i) || d_i isa AbstractZero) && return zero(A.u[idx])
d_i
Expand All @@ -98,6 +103,8 @@ function vofa_u_adjoint(d, A::RecursiveArrayTools.AbstractVectorOfArray)
end

function vofa_u_adjoint(d, A::RecursiveArrayTools.AbstractDiffEqArray)
all(d_i -> isnothing(d_i) || d_i isa Union{AbstractZero, AbstractArray, Number}, d) ||
return (; u = collect(d))
m = map(enumerate(d)) do (idx, d_i)
(isnothing(d_i) || d_i isa AbstractZero) && return zero(A.u[idx])
d_i
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21 changes: 21 additions & 0 deletions test/AD/adjoints.jl
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Expand Up @@ -118,3 +118,24 @@ let ext = Base.get_extension(RecursiveArrayTools, :RecursiveArrayToolsZygoteExt)
@test g_dea.u == expected
@test g_dea.t == dea.t
end

# Structural per-element cotangents (e.g. the per-solution NamedTuple tangents
# produced when differentiating `ensemble_sol.u`) cannot be stored in a
# VectorOfArray; the `u`-field tangent is returned instead
# (SciML/DifferentialEquations.jl#1149).
let ext = Base.get_extension(RecursiveArrayTools, :RecursiveArrayToolsZygoteExt)
voa = VectorOfArray([Float64[i, i, i] for i in 1:3])
dea = DiffEqArray([Float64[i, i, i] for i in 1:3], 1:3)
d = Any[
(; u = Float64[1, 1, 1], t = 0.5), nothing,
(; u = Float64[3, 3, 3], t = 0.25),
]

g_voa = ext.vofa_u_adjoint(d, voa)
@test g_voa isa NamedTuple
@test g_voa.u == collect(d)

g_dea = ext.vofa_u_adjoint(d, dea)
@test g_dea isa NamedTuple
@test g_dea.u == collect(d)
end
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