Efficient, reliable computation of resonances of the one-dimensional Schroedinger equation

We present a numerical method, implemented in a Fortran code RESON, for computing resonance of the radial one-dimensional Schroedinger equation, for an underlying potential that decays sufficiently fast at infinity. The basic approach is to maximize the time-delay function [tau]([lambda]) as in the LeRoy program TDELAY. We present some theory that allows a preliminary bracketing of the resonance and various ways of reducing the total work. Together with automatic meshsize selection this leads to a method that has proved efficient, robust, and extremely trouble-free in numerical tests. The code makes use of Marletta's Sturm-Liouville solver, SLO2F, due to go into the NAG library. 24 refs., 4 figs., 3 tabs.