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Define copyto! for GPU Diagonals #829

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Merged
maleadt merged 2 commits into from
Oct 28, 2026
Merged

Define copyto! for GPU Diagonals #829

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11c0d7f
Copy only the diagonal in copyto!(::Diagonal, ::Diagonal) for GPU arrays
christiangnrd Oct 20, 2026
e04e656
Test `copyto!` between GPU Diagonals
maleadt Oct 27, 2026
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8 changes: 8 additions & 0 deletions src/host/linalg.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -326,6 +326,14 @@ end

Base.copy(D::Diagonal{T, <:AbstractGPUArray{T, N}}) where {T, N} = Diagonal(copy(D.diag))

# copy only the diagonal; the generic `AnyGPUArray` method would launch a kernel over all
# n^2 entries, calling `setindex!(::Diagonal, ...)` whose error path isn't GPU-compatible
function Base.copyto!(D1::Diagonal{T, <:AbstractGPUArray{T, N}},
D2::Diagonal{S, <:AbstractGPUArray{S, M}}) where {T, N, S, M}
copyto!(D1.diag, D2.diag)
return D1
end

_isrealandpositive(x) = isreal(x) && real(x) > 0

function LinearAlgebra.cholesky!(D::Diagonal{<:Any, <:AbstractGPUArray},
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12 changes: 12 additions & 0 deletions test/testsuite/linalg.jl
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Expand Up @@ -512,6 +512,18 @@ end
@test collect(D) == collect(C)
end

@testset "copyto! diagonal" begin
D = Diagonal(AT(rand(Float32, 10)))
C = Diagonal(AT(zeros(Float32, 10)))
@test copyto!(C, D) === C
@test C.diag isa AT
@test collect(C) == collect(D)

D = Diagonal(AT(Int32.(1:10)))
copyto!(C, D)
@test collect(C) == Diagonal(Float32.(1:10))
end

@testset "cholesky + Diagonal" begin
n = 128
# Add one in order prevent failures due to random numbers being zero
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