tr, and tests

Author: ZeppLu

stdlib/LinearAlgebra/src/uniformscaling.jl

@@ -161,6 +161,14 @@ function det(J::UniformScaling{T}) where T
     end
 end
 
+function tr(J::UniformScaling{T}) where T
+    if iszero(J.λ)
+        zero(T)
+    else
+        throw(ArgumentError("Trace of UniformScaling is only well-defined when λ = 0"))
+    end
+end
+
 *(J1::UniformScaling, J2::UniformScaling) = UniformScaling(J1.λ*J2.λ)
 *(B::BitArray{2}, J::UniformScaling) = *(Array(B), J::UniformScaling)
 *(J::UniformScaling, B::BitArray{2}) = *(J::UniformScaling, Array(B))

stdlib/LinearAlgebra/test/uniformscaling.jl

@@ -126,7 +126,11 @@ end
     @test (2I)^α == (2I).^α == (2^α)I
 end
 
-@testset "det and logdet" begin
+@testset "tr, det and logdet" begin
+    for T in (Int, Float64, ComplexF64, Bool)
+        @test tr(UniformScaling(zero(T))) === zero(T)
+    end
+    @test_throws ArgumentError tr(UniformScaling(1))
     @test det(I) === true
     @test det(1.0I) === 1.0
     @test det(0I) === 0