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Manuscript Title: RAD-TRAP 2, a program for the solution of the Holstein equation of radiation trapping.
Authors: A.F. Molisch, B.P. Oehry, W. Schupita, G. Magerl
Program title: RAD-TRAP 2
Catalogue identifier: ACLB_v2_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 77(1993)255
Programming language: Fortran.
Computer: VAX 3100.
Operating system: VMS, MS-DOS 5.0.
RAM: 500K words
Word size: 32
Keywords: Trapping radiation, Radiative transfer, Fredholm integral Equations, Lifetime measurements, Lineshape measurements, Eigenvalues, Steady-state Distribution of excited Atoms, Emergent spectra.
Classification: 21.2.

Nature of problem:
Computation of the eigenvalues and eigenfunctions of the Holstein integral equation (describing radiation trapping in an atomic vapor) and the steady-state distribution of excited atoms in one-dimensional geometries.

Solution method:
Reduction of the Fredholm integral equation of the second kind to an algebraic system of equations which is solved by standard methods.

Reasons for new version:
We have developed a new algorithm for the computation of the matrix elements for all the computations in the cylinder case; this new algorithm offers very high accuracy at still reasonable run time. Furthermore, the computation of the steady-state distribution of excited atoms and the computation of the emergent spectra are additional convenient features. The new version requires fewer NAGLIB routines and thus can be run also on a PC.

Restrictions:
Restrictions of the achievable accuracy by memory and run-time limitations.

Unusual features:
Uses subroutines from a standard library of mathematical subprograms, NAGLIB. The program is divided into 6 modules that must be compiled and linked separately.

Running time:
Strongly dependent on the chosen geometry, the lineshape, the opacity and especially the required accuracy; will be between 1 and 1000 CPU seconds in most practical cases on a VAX 3100, or an IBM-PC (486/66MHz).