Suppose I have 2 domains(3D) : V_in (finite domain) surrounded by V_out (infinite domain) and I want to solve
1. Poisson equation in V_in
and 2. Laplace equation in V_out
The boundary condition at infinity is the solution is zero at infinity. (or to be more precise http://en.wikipedia.org/wiki/Sommerfeld_radiation_condition)
Is there a way FEM can impose this boundary condition without making the box (infinite domain) very very large and V_in very small.