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Fix nested ForwardDiff tag mismatch #3406

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Fix nested ForwardDiff tag mismatch #3406

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18 changes: 18 additions & 0 deletions lib/DiffEqBase/ext/DiffEqBaseForwardDiffExt.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -204,6 +204,24 @@ if !hasmethod(nextfloat, Tuple{ForwardDiff.Dual})
end
end

struct WidenedDualArray{T,A} <: AbstractVector{T}
parent::A
end
Base.size(a::WidenedDualArray) = size(a.parent)
Base.@propagate_inbounds Base.getindex(a::WidenedDualArray{T}, i::Int) where {T} = convert(T, a.parent[i])

function (ff::SciMLBase.UJacobianWrapper{true})(du1, uprev::AbstractArray{<:ForwardDiff.Dual})
p = ff.p
if p isa AbstractArray && eltype(p) <: ForwardDiff.Dual
DualU = eltype(uprev)
if !(eltype(p) <: DualU)
hasfield(typeof(ff.f), :f) && getfield(ff.f, :f) isa FunctionWrappersWrappers.FunctionWrappersWrapper && return ff.f(du1, uprev, p, ff.t)
Comment on lines +213 to +218
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@ChrisRackauckas ChrisRackauckas Apr 12, 2026

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No need to do it like this, it should just be in the solve dispatch?

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@AdityaPandeyCN AdityaPandeyCN Apr 13, 2026

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I tried it but the DiffEqBase solve path can't promote p because the nested dual type doesn't exist yet at that point , it's created later by Rosenbrock's JacobianConfig. Promoting early caused triple nesting.

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@ChrisRackauckas ChrisRackauckas Apr 13, 2026

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It's incorrect to just unwrap the functionwrapper though, that means the wrong call is getting compiled, so it needs to be handled at the source of the issue.

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@AdityaPandeyCN AdityaPandeyCN Apr 13, 2026

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Makes sense. I'll move the fix to jacobian! in derivative_wrappers.jl , widen p once before DI.jacobian! runs, same approach as #3389. or you could reopen that.

return ff.f(du1, uprev, WidenedDualArray{DualU, typeof(p)}(p), ff.t)
end
end
ff.f(du1, uprev, p, ff.t)
end

import PrecompileTools
PrecompileTools.@compile_workload begin
# Scalar operations on Dual numbers (arithmetic, math functions, comparisons)
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