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Aggressive constprop in trevc! to stabilize triangular eigvec (#54635)
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We may use aggressive constprop in `trevc!` to eliminate branches, which
makes the return type of `eigvec(::UpperTriangular)` concretely
inferred.
```julia
julia> @inferred eigvecs(UpperTriangular([1 0; 0 1]))
2×2 Matrix{Float32}:
 1.0  -0.0
 0.0   1.0
```

(cherry picked from commit ea8b4af)
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jishnub authored and KristofferC committed Jun 19, 2024
1 parent 3f35094 commit e52719b
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Showing 2 changed files with 7 additions and 1 deletion.
2 changes: 1 addition & 1 deletion stdlib/LinearAlgebra/src/lapack.jl
Original file line number Diff line number Diff line change
Expand Up @@ -3633,7 +3633,7 @@ for (trcon, trevc, trrfs, elty) in
# LOGICAL SELECT( * )
# DOUBLE PRECISION T( LDT, * ), VL( LDVL, * ), VR( LDVR, * ),
#$ WORK( * )
function trevc!(side::AbstractChar, howmny::AbstractChar, select::AbstractVector{BlasInt}, T::AbstractMatrix{$elty},
Base.@constprop :aggressive function trevc!(side::AbstractChar, howmny::AbstractChar, select::AbstractVector{BlasInt}, T::AbstractMatrix{$elty},
VL::AbstractMatrix{$elty} = similar(T),
VR::AbstractMatrix{$elty} = similar(T))
require_one_based_indexing(select, T, VL, VR)
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6 changes: 6 additions & 0 deletions stdlib/LinearAlgebra/test/triangular.jl
Original file line number Diff line number Diff line change
Expand Up @@ -879,4 +879,10 @@ end
@test transpose!(U) == Ut
end

@testset "type-stable eigvecs" begin
D = Float64[1 0; 0 2]
V = @inferred eigvecs(UpperTriangular(D))
@test V == Diagonal([1, 1])
end

end # module TestTriangular

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