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Manuscript Title: A program for calculating Regge trajectories in potential scattering.
Authors: P.G. Burke, C. Tate
Catalogue identifier: AAGA_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 1(1969)97
Programming language: Fortran.
Computer: I.C.L.1907.
Operating system: QUBE.
RAM: 11K words
Word size: 24
Keywords: Nuclear physics, Phase shift, Bound state, Regge, Bessel function, Eigenvalue, Schrodinger, Complex, Gamma function, Yukawa potential, Trajectory, S-matrix, Scattering, Pole, Angular momentum, Optical model.
Classification: 17.9.

Nature of problem:
This program solves the radial Schrodinger equation and finds the positions and residues of Regge poles for a Yukawa potential and follows these poles automatically as a function of energy. Alternatively, it will compute the S-matrix and phase shifts at a specified grid of points in the complex angular momentum plane and for a given set of energies. The program can be modified to calculate Regge trajectories for any potential which can be specified by an analytic formula.

Solution method:
The radial Schrodinger equation is integrated numerically inwards and outwards using the Runge-Kutta-Gill method. The S-matrix is determined by fitting the solution to a complex Bessel function, and the poles in the S-matrix are found by Newton's iteration method.

The program is limited to real positive and negative values of the energy and to all complex angular momenta except the half odd integers.

Running time:
The evaluation of the S-matrix at one point takes about six seconds on the ICL 1907. To determine the position of a pole in the S-matrix takes about 40 seconds for a typical number of iterations.