Call symmetry check function instead of checking type

Author: jishnub

src/symmetric.jl

@@ -441,6 +441,10 @@ issymmetric(A::Hermitian{<:Real}) = true
 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(::Any) = false
+
 adjoint(A::Hermitian) = A
 transpose(A::Symmetric) = A
 adjoint(A::Symmetric{<:Real}) = A

src/tridiag.jl

@@ -111,7 +111,7 @@ function (::Type{SymTri})(A::AbstractMatrix) where {SymTri <: SymTridiagonal}
     checksquare(A)
     du = diag(A, 1)
     d  = diag(A)
-    if !(A isa Symmetric || _checksymmetric(d, du, diag(A, -1)))
+    if !(_issymmetric(A) || _checksymmetric(d, du, diag(A, -1)))
         throw(ArgumentError("matrix is not symmetric; cannot convert to SymTridiagonal"))
     end
     return SymTri(d, du)