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Manuscript Title: I-NoLLS: a program for interactive non-linear least-squares fitting of the parameters of physical models.
Authors: M.M. Law, J.M. Hutson
Program title: I-NoLLS
Catalogue identifier: ADFN_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 102(1997)252
Programming language: Fortran.
Computer: IBM RS/6000.
Operating system: Unix.
Peripherals: disc.
Keywords: General purpose, Fit, Molecular physics, Interactive, Non-linear least-squares, Molecular potential Energy surface, Optimization, Model fitting.
Classification: 4.9.

Nature of problem:
I-NoLLS permits interactive least-squares fitting of the parameters of analytical models to physical properties or other data.

Solution method:
A variety of algorithms adapted to non-linear least-squares optimization are used, including: Gauss-Newton [1], Levenberg-Marquardt [2,3] and Singular Value Analysis based [4] algorithms. The interactive nature of the code permits rapid and flexible user control over the progress of the fit.

Restrictions:
none

Unusual features:
The user must supply a subroutine that calculates theoretical values of the quantities to be fitted and their first partial derivatives with respect to the adjustable parameters. The Application Visualisation System (AVS) [5] is required to provide the user interface.

Running time:
problem-dependent

References:
[1] P.R. Bevington, Data Reduction and Error Analysis for the Physical Sciences (McGraw-Hill, London, 1969).
[2] K. Levenberg, Quart. Appl. Math. 2(1994)164.
[3] D. Marquardt, SIAM J. Appl. Math. 11(1963)431.
[4] C.L. Lawson and R.J. Hanson, Solving Least Squares Problems (Prentice-Hall, New Jersey, 1974).
[5] Application Visualisation System computer code, release 5.0 (distributed by Advanced Visual Systems Inc., USA, 1993).