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avoid division by zero in svd(::Diagonal) #1150

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Dec 22, 2024
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avoid division by zero in svd(::Diagonal) #1150

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1e6183b
avoid division by zero in svd(::Diagonal)
araujoms Dec 15, 2024
bb5f566
add test
araujoms Dec 16, 2024
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4 changes: 2 additions & 2 deletions src/diagonal.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -1024,8 +1024,8 @@ function svd(D::Diagonal{T}) where {T<:Number}
Vt = copy(U)
for i in 1:length(d)
j = piv[i]
U[j,i] = d[j] / S[i]
Vt[i,j] = one(Td)
U[j,i] = iszero(d[j]) ? oneunit(Td) : d[j] / S[i]
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Vt[i,j] = oneunit(Td)
end
return SVD(U, S, Vt)
end
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3 changes: 2 additions & 1 deletion test/diagonal.jl
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Expand Up @@ -463,7 +463,8 @@ Random.seed!(1)
end
end

@testset "svd (#11120/#11247)" begin
@testset "svd (#11120/#11247/#1149)" begin
D[1] = 0
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Is this changing D for all the tests coming after this? I see that tests pass, but perhaps it's better to introduce a small new testset with the example you gave in the original issue:

d = [1, 2, 3, 4, 0]
@test svd(diagm(d)) == svd(Diagonal(d))

?

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Indeed, it is. That was intentional, as the subsequent test was also failing for singular matrices. I thought about doing that when D is generated in the first place, as a zero is more useful test than a random number, but decided against because that would be confusing.

I don't have anything to do with issue, though, I just randomly found it and decided to fix it because it was so easy.

U, s, V = svd(D)
@test (U*Diagonal(s))*V' ≈ D
@test svdvals(D) == s
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