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Unthunk cotangent components in findnz pullbacks #843

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Unthunk cotangent components in findnz pullbacks #843

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2 changes: 2 additions & 0 deletions src/rulesets/SparseArrays/sparsematrix.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@ function rrule(::typeof(findnz), A::AbstractSparseMatrix)

function findnz_pullback(Δ)
_, _, V̄ = unthunk(Δ)
V̄ = unthunk(V̄)
V̄ isa AbstractZero && return (NoTangent(), V̄)
return NoTangent(), sparse(I, J, V̄, m, n)
end
Expand All @@ -43,6 +44,7 @@ function rrule(::typeof(findnz), v::AbstractSparseVector)

function findnz_pullback(Δ)
_, V̄ = unthunk(Δ)
V̄ = unthunk(V̄)
V̄ isa AbstractZero && return (NoTangent(), V̄)
return NoTangent(), sparsevec(I, V̄, n)
end
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8 changes: 8 additions & 0 deletions test/rulesets/SparseArrays/sparsematrix.jl
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Expand Up @@ -77,6 +77,14 @@ end
I, V = findnz(v)
V̄ = rand!(similar(V))
test_rrule(findnz, v ⊢ dv, output_tangent=(zeros(length(I)), V̄))

# cotangent components may be thunks
IA, JA, VA = findnz(A)
V̄A = rand!(similar(VA))
_, pb = rrule(findnz, A)
@test pb((ZeroTangent(), ZeroTangent(), @thunk(V̄A)))[2] == sparse(IA, JA, V̄A, 5, 5)
_, pb = rrule(findnz, v)
@test pb((ZeroTangent(), @thunk(V̄)))[2] == sparsevec(I, V̄, 5)
end

if Base.USE_GPL_LIBS # these rrules don't work without CHOLMOD from SuiteSparse.jl
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