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Let cond of an empty square matrix return zero #1169

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Jan 29, 2025
Merged

Let cond of an empty square matrix return zero #1169

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602578d
Let `cond` of an empty square matrix return zero
martinholters Nov 10, 2020
3142a5e
DRY up test with `for` loops
martinholters Jan 27, 2025
507cb3b
Rename `norm` to `p` in tests
martinholters Jan 28, 2025
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4 changes: 4 additions & 0 deletions src/dense.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -1779,6 +1779,10 @@ Condition number of the matrix `M`, computed using the operator `p`-norm. Valid
"""
function cond(A::AbstractMatrix, p::Real=2)
if p == 2
if isempty(A)
checksquare(A)
return zero(real(eigtype(eltype(A))))
end
v = svdvals(A)
maxv = maximum(v)
return iszero(maxv) ? oftype(real(maxv), Inf) : maxv / minimum(v)
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12 changes: 12 additions & 0 deletions test/dense.jl
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Expand Up @@ -56,6 +56,18 @@ Random.seed!(1234323)
@test cond(Mars, 2) ≈ 6.181867355918493
@test cond(Mars, Inf) ≈ 7.1
end
@testset "Empty matrices" begin
for p in (1,2,Inf)
# zero for square (i.e. 0×0) matrices
@test cond(zeros(Int, 0, 0), p) === 0.0
@test cond(zeros(0, 0), p) === 0.0
@test cond(zeros(ComplexF64, 0, 0), p) === 0.0
# error for non-square matrices
for size in ((10,0), (0,10))
@test_throws DimensionMismatch cond(zeros(size...), p)
end
end
end
end

areal = randn(n,n)/2
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