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Fix transpose(A) * Diagonal products for non-commutative eltypes #1753

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dkarrasch merged 2 commits into from
Oct 11, 2026
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Fix transpose(A) * Diagonal products for non-commutative eltypes #1753

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0c64e4f
Fix transpose(A) * Diagonal products for non-commutative eltypes
claude Oct 10, 2026
46a0285
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dkarrasch Oct 11, 2026
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8 changes: 8 additions & 0 deletions src/diagonal.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -346,14 +346,20 @@ function (*)(D::Diagonal, V::AbstractVector)
return D.diag .* V
end

_wrapperop_reverses_products(::Adjoint, ::Diagonal) = true
_wrapperop_reverses_products(::Transpose{<:Union{Real,Complex}}, ::Diagonal{<:Union{Real,Complex}}) = true
_wrapperop_reverses_products(A, D) = false

function mul(A::AdjOrTransAbsMat, D::Diagonal)
_wrapperop_reverses_products(A, D) || return @invoke mul(A::AbstractMatrix, D::AbstractMatrix)
adj = _wrapperop(A)
copy(adj(adj(D) * adj(A)))
end
function mul(A::AdjOrTransAbsMat{<:Number, <:StridedMatrix}, D::Diagonal{<:Number})
@invoke mul(A::AbstractMatrix, D::AbstractMatrix)
end
function mul(D::Diagonal, A::AdjOrTransAbsMat)
_wrapperop_reverses_products(A, D) || return @invoke mul(D::AbstractMatrix, A::AbstractMatrix)
adj = _wrapperop(A)
copy(adj(adj(A) * adj(D)))
end
Expand All @@ -374,6 +380,7 @@ end
# A' = A' * D => A = D' * A
# This uses the fact that D' is a Diagonal
function rmul!(A::AdjOrTransAbsMat, D::Diagonal)
_wrapperop_reverses_products(A, D) || return @invoke rmul!(A::AbstractMatrix, D::Diagonal)
f = _wrapperop(A)
lmul!(f(D), f(A))
A
Expand Down Expand Up @@ -421,6 +428,7 @@ end
# A' = D * A' => A = A * D'
# This uses the fact that D' is a Diagonal
function lmul!(D::Diagonal, A::AdjOrTransAbsMat)
_wrapperop_reverses_products(A, D) || return @invoke lmul!(D::Diagonal, A::AbstractVecOrMat)
f = _wrapperop(A)
rmul!(f(A), f(D))
A
Expand Down
14 changes: 14 additions & 0 deletions test/diagonal.jl
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Expand Up @@ -16,6 +16,7 @@ using Main.LinearAlgebraTestHelpers.InfiniteArrays
using Main.LinearAlgebraTestHelpers.FillArrays
using Main.LinearAlgebraTestHelpers.SizedArrays
using Main.LinearAlgebraTestHelpers.ImmutableArrays
using Main.LinearAlgebraTestHelpers.Quaternions

const n=12 # Size of matrix problem to test
Random.seed!(1)
Expand Down Expand Up @@ -1633,4 +1634,17 @@ end
end
end

@testset "products of Diagonal with transposed non-commutative matrices (issue #1750)" begin
i, j, k = Quaternion(0.0,1,0,0), Quaternion(0.0,0,1,0), Quaternion(0.0,0,0,1)
M = [i j; zero(i) k]
A = view(M, [1, 2], :)
D = Diagonal([j, k])
for op in (transpose, adjoint)
@test op(A) * D == Matrix(op(A)) * D
@test D * op(A) == D * Matrix(op(A))
@test rmul!(op(copy(M)), D) == Matrix(op(M)) * D
@test lmul!(D, op(copy(M))) == D * Matrix(op(M))
end
end

end # module TestDiagonal
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