An algorithm for separable representations of realistic interactions

A general method for expanding in a separable form a local interaction is developed. The algorithm makes use of the Gamow vectors and momenta, calculated from an eigenvalue problem, and preserves the analytic properties of the original S-matrix. Applications are presented for realistic nucleon-nucleon interactions and phenomenological optical potentials. The agreement between the separable and exact scattering matrices is quite good on and off the energy shell, for a wide range of energies.