[kingmaker]

Hello
I am trying to implement a small FEM code for solving Poisson equation on arbitrary domains. I understand how to implement Drichlet Boundary conditions after formulating the Global stiffness matrix.

But I do not quite understand how to implement Neumann Boundary conditions. For example I have to integrate over the the boundary of the element. But what if a particular element does not have a boundary, like its completely in the interior.

Also when we integrate over the boundary what should be done when a element has only one of its nodes on the boundary ?

Thanks in advance