  We critically review the fast algorithms for the numerical study of
two--dimensional Josephson junction arrays and develop the analogy of such
systems with electrostatics. We extend these procedures to arrays with
bus--bars and defects in the form of missing bonds. The role of boundaries and
of the guage choice in determing the Green's function of the system is
clarified. The extension of the Green's function approach to other situations
is also discussed.
