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Let cond of an empty matrix return zero #38372

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Let cond of an empty matrix return zero #38372

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1 change: 1 addition & 0 deletions stdlib/LinearAlgebra/src/dense.jl
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Expand Up @@ -1456,6 +1456,7 @@ Condition number of the matrix `M`, computed using the operator `p`-norm. Valid
"""
function cond(A::AbstractMatrix, p::Real=2)
if p == 2
isempty(A) && return zero(real(eigtype(eltype(A))))
v = svdvals(A)
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maxv = maximum(v)
return iszero(maxv) ? oftype(real(maxv), Inf) : maxv / minimum(v)
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13 changes: 13 additions & 0 deletions stdlib/LinearAlgebra/test/dense.jl
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Expand Up @@ -39,6 +39,19 @@ Random.seed!(1234321)
M = [1.0 -2.0; -2.0 -1.5]
@test cond(M, 1) ≈ 2.227272727272727
end
@testset "Empty matrices" begin
@test cond(zeros(Int, 0, 0), 1) === 0.0
@test cond(zeros(Int, 0, 0), 2) === 0.0
@test cond(zeros(Int, 0, 0), Inf) === 0.0
@test cond(zeros(0, 0), 1) === 0.0
@test cond(zeros(0, 0), 2) === 0.0
@test cond(zeros(0, 0), Inf) === 0.0
@test cond(zeros(ComplexF64, 0, 0), 1) === 0.0
@test cond(zeros(ComplexF64, 0, 0), 2) === 0.0
@test cond(zeros(ComplexF64, 0, 0), Inf) === 0.0
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@test cond(zeros(10, 0)) === 0.0
@test cond(zeros(0, 10)) === 0.0
end
end

areal = randn(n,n)/2
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