added parent adjoint for LowerTriangular and UpperTriangular

Author: torfjelde

src/lib/array.jl

@@ -355,6 +355,8 @@ end
 
 @adjoint parent(x::LinearAlgebra.Adjoint) = parent(x), ȳ -> (LinearAlgebra.Adjoint(ȳ),)
 @adjoint parent(x::LinearAlgebra.Transpose) = parent(x), ȳ -> (LinearAlgebra.Transpose(ȳ),)
+@adjoint parent(x::LinearAlgebra.UpperTriangular) = parent(x), ȳ -> (LinearAlgebra.UpperTriangular(ȳ),)
+@adjoint parent(x::LinearAlgebra.LowerTriangular) = parent(x), ȳ -> (LinearAlgebra.LowerTriangular(ȳ),)
 
 function _kron(mat1::AbstractMatrix,mat2::AbstractMatrix)
     m1, n1 = size(mat1)