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Manuscript Title: Extracting S-matrix poles for resonances from numerical scattering data: type-II Padé reconstruction
Authors: D. Sokolovski, E. Akhmatskaya, S.K. Sen
Program title: PADE II
Catalogue identifier: AEHO_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 182(2011)448
Programming language: FORTRAN 77.
Computer: Any computer equipped with a FORTRAN 90 compiler.
Operating system: UNIX, LINUX.
RAM: 256 Mb
Keywords: Resonances, S-matrix, Padé approximation, Regge-poles.
PACS: 34.50.Lf, 34.50.Pi.
Classification: 16.8.

External routines: NAG Program Library (http://www.nag.co.uk/numeric/fl/FLdescription.asp)

Nature of problem:
The package extracts the positions and residues of resonance poles from numerical scattering data supplied by the user. The data can then be used for quantitative analysis of interference patterns observed in elastic, inelastic and reactive integral and differential cross sections.

Solution method:
The S-matrix element is analytically continued in the complex plane of either energy or angular momentum with the help of Padé approximation of type II. Resonance (complex energy or Regge) poles are identified and their residues evaluated.

Unusual features:
Use of multiple precision MPFUN package [1]. (Distributed with the PADE II code).

Running time:
From several seconds to several minutes depending on the precision level chosen and the number of iterations performed.

[1] D. H. Bailey, Algorithm 719, Multiprecision translation and execution of Fortran programs . ACM Transactions on Mathematical Software, 19(3), (1993) 288.