Finite-element method for computing scattering phase shifts from discrete models

A method is described which converts the dense distribution of pole singularities given by a discrete representation of a Green's function or resolvent operator into an approximation to the smooth function defined by the continuum limit of such a representation. The method uses a finite-element approximation to the pole-strength distribution function, equivalent to the width function in a scattering problem. Three distinct applications of this method are provided by a model scattering problem, making use of Feshbach resonance theory, the Schwinger variational principle, and the theory of the Fredholm determinant, respectively. © 1981 The American Physical Society.