Hi all, Generally boundary condition (Dirichlet and Neumann) are applied on the Load Vector, in FEM formulation. The equation i solved, is Generalized eigenvalue equation for Scalar Helmholtz equation in homogeneous wave guide with perfectly conducting wall ( Kψ =λMψ ), and found, doesn't need to apply boundary condition as here, i encounter natural boundary condition. I want to apply this equation for anisotropic, inhomogeneous medium, and read that, i have to use vector fem with edge element and not nodal element that i used in my procedure, to avoid non physical solution (spurious mode). and here boundary condition are necessary, now i confused, how to apply boundary condition if there is no Load vector in formulation? and as per my reading, there is no way to apply BC on Stiffness and Mass matrix. thanks in advance.