Tests for LinearAlgebra.powm (#35101)

Co-authored-by: Daniel Karrasch <Daniel.Karrasch@gmx.de>
JuliaLang · Apr 11, 2020 · 1547522 · 1547522
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diff --git a/stdlib/LinearAlgebra/src/triangular.jl b/stdlib/LinearAlgebra/src/triangular.jl
@@ -2180,7 +2180,7 @@ end
 #     34(3), (2013) 1341–1360.
 function powm!(A0::UpperTriangular{<:BlasFloat}, p::Real)
     if abs(p) >= 1
-        ArgumentError("p must be a real number in (-1,1), got $p")
+        throw(ArgumentError("p must be a real number in (-1,1), got $p"))
     end
 
     normA0 = opnorm(A0, 1)
@@ -2239,7 +2239,7 @@ function powm!(A0::UpperTriangular{<:BlasFloat}, p::Real)
     rmul!(S, normA0^p)
     return S
 end
-powm(A::LowerTriangular, p::Real) = copy(transpose(powm(copy(transpose(A)), p::Real)))
+powm(A::LowerTriangular, p::Real) = copy(transpose(powm!(copy(transpose(A)), p::Real)))
 
 # Complex matrix logarithm for the upper triangular factor, see:
 #   Al-Mohy and Higham, "Improved inverse  scaling and squaring algorithms for

diff --git a/stdlib/LinearAlgebra/test/triangular.jl b/stdlib/LinearAlgebra/test/triangular.jl
@@ -641,4 +641,14 @@ end
     end
 end
 
+@testset "Error condition for powm" begin
+    A = UpperTriangular(rand(ComplexF64, 10, 10))
+    @test_throws ArgumentError LinearAlgebra.powm!(A, 2.2)
+    A = LowerTriangular(rand(ComplexF64, 10, 10))
+    At = copy(transpose(A))
+    p = rand()
+    @test LinearAlgebra.powm(A, p) == transpose(LinearAlgebra.powm!(At, p))
+    @test_throws ArgumentError LinearAlgebra.powm(A, 2.2)
+end
+
 end # module TestTriangular