Let cond of an empty matrix return zero

Fixes #38327.
JuliaLang · Nov 10, 2020 · 6efb075 · 6efb075
1 parent 21c2c51
commit 6efb075
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diff --git a/stdlib/LinearAlgebra/src/dense.jl b/stdlib/LinearAlgebra/src/dense.jl
@@ -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)
         maxv = maximum(v)
         return iszero(maxv) ? oftype(real(maxv), Inf) : maxv / minimum(v)

diff --git a/stdlib/LinearAlgebra/test/dense.jl b/stdlib/LinearAlgebra/test/dense.jl
@@ -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
+        @test cond(zeros(10, 0)) === 0.0
+        @test cond(zeros(0, 10)) === 0.0
+    end
 end
 
 areal = randn(n,n)/2