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Fix multiplication with empty HessenbergQ #1326

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Merged
merged 1 commit into from
May 1, 2025
Merged

Fix multiplication with empty HessenbergQ #1326

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5 changes: 3 additions & 2 deletions src/lapack.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -6135,10 +6135,11 @@
chkside(side)
chktrans(trans)
n = checksquare(A)
ntau = length(tau)
mC, nC = size(C, 1), size(C, 2)

if n - length(tau) != 1
throw(DimensionMismatch(lazy"tau has length $(length(tau)), needs $(n - 1)"))
if max(n - 1, 0) != ntau
throw(DimensionMismatch(lazy"tau has length $ntau, needs $(n - 1)"))

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end
if (side == 'L' && mC != n) || (side == 'R' && nC != n)
throw(DimensionMismatch("A and C matrices are not conformable"))
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7 changes: 7 additions & 0 deletions test/hessenberg.jl
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Expand Up @@ -286,4 +286,11 @@ end
end
end

@testset "multiplication with empty HessenbergQ" begin
@test ones(2, 0)*hessenberg(zeros(0,0)).Q == zeros(2,0)
@test_throws DimensionMismatch ones(2, 1)*hessenberg(zeros(0,0)).Q
@test hessenberg(zeros(0,0)).Q * ones(0, 2) == zeros(0,2)
@test_throws DimensionMismatch hessenberg(zeros(0,0)).Q * ones(1, 2)
end

end # module TestHessenberg