Add cond method for UniformScaling (#19906)

* cond method for UniformScaling with tests

base/linalg/uniformscaling.jl

@@ -1,6 +1,6 @@
 # This file is a part of Julia. License is MIT: https://julialang.org/license
 
-import Base: copy, ctranspose, getindex, show, transpose, one, zero, inv,
+import Base: cond, copy, ctranspose, getindex, show, transpose, one, zero, inv,
  @_pure_meta, hcat, vcat, hvcat
 import Base.LinAlg: SingularException
 
@@ -178,6 +178,11 @@ function copy!(A::AbstractMatrix, J::UniformScaling)
  return A
 end
 
+function cond{T}(J::UniformScaling{T})
+ onereal = inv(one(real(J.λ)))
+ return J.λ ≠ zero(T) ? onereal : oftype(onereal, Inf)
+end
+
 # promote_to_arrays(n,k, T, A...) promotes any UniformScaling matrices
 # in A to matrices of type T and sizes given by n[k:end]. n is an array
 # so that the same promotion code can be used for hvcat. We pass the type T

test/linalg/uniformscaling.jl

@@ -49,6 +49,8 @@ J = UniformScaling(λ)
  @test I + I === UniformScaling(2) # +
  @test inv(I) == I
  @test inv(J) == UniformScaling(inv(λ))
+ @test cond(I) == 1
+ @test cond(J) == (λ ≠ zero(λ) ? one(real(λ)) : oftype(real(λ), Inf))
 end
 
 B = bitrand(2,2)