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Manuscript Title: The program LOPT for least-squares optimization of energy levels
Authors: A.E. Kramida
Program title: LOPT
Catalogue identifier: AEHM_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 182(2011)419
Programming language: Perl v.5.
Computer: PC, Mac, Unix workstations.
Operating system: MS Windows (XP, Vista, 7), Mac OS X, Linux, Unix (AIX).
RAM: 3 Mwords or more
Word size: 32 or 64
Keywords: atomic energy levels, Ritz wavelengths, least-squares optimization.
PACS: 02.60.Pn, 32.10.Fn, 32.30.-r, 32.30.Bv, 32.30.Jc, 33.15.Pw, 33.20.Kf, 33.20.Lg, 33.20.Ni.
Classification: 2.2.

Nature of problem:
The least-squares energy-level optimization problem, i.e., finding a set of energy level values that best fits the given set of transition intervals.

Solution method:
The solution of the least-squares problem is found by solving the corresponding linear matrix equation, where the matrix is constructed using a new method with variable substitution.

Restrictions:
A practical limitation on the size of the problem N is imposed by the execution time, which scales as N3 and depends on the computer.

Unusual features:
Properly rounds the resulting data and formats the output in a format suitable for viewing with spreadsheet editing software. Estimates numerical errors resulting from the limited machine precision.

Running time:
1 sec for N = 100, or 60 sec for N = 400 on a typical PC.