_issymetric for SymTridiagonal

Author: jishnub

src/symmetric.jl

@@ -442,7 +442,7 @@ issymmetric(A::Hermitian{<:Complex}) = isreal(A)
 issymmetric(A::Symmetric) = true
 
 # check if the symmetry is known from the type
-_issymmetric(::Union{Symmetric, Hermitian{<:Real}}) = true
+_issymmetric(::Union{SymSymTri, Hermitian{<:Real}}) = true
 _issymmetric(::Any) = false
 
 adjoint(A::Hermitian) = A

test/tridiag.jl

@@ -1174,6 +1174,10 @@ end
 
 @testset "SymTridiagonal from Symmetric" begin
     S = Symmetric(reshape(1:9, 3, 3))
+    @testset "helper functions" begin
+        @test LinearAlgebra._issymmetric(S)
+        @test !LinearAlgebra._issymmetric(Array(S))
+    end
     ST = SymTridiagonal(S)
     @test ST == SymTridiagonal(diag(S), diag(S,1))
 end