I-NOLLS - A PROGRAM FOR INTERACTIVE NONLINEAR LEAST-SQUARES FITTING OF THE PARAMETERS OF PHYSICAL MODELS

The I-NoLLS program is a package for carrying out interactive nonlinea r least-squares fits to determine the parameters of physical or mathem atical models from experimental or other data, under circumstances whe re automated least-squares procedures are excessively computationally expensive and the user needs interactive control to apply physical ins ight to the fitting process. The program was developed to facilitate t he fitting of molecular potential energy surfaces (PES) to spectroscop ic and scattering data, but is also applicable to a variety of other o ptimization problems. A range of different algorithms adapted to highl y nonlinear least-squares problems may be selected. The interactive na ture of the code permits rapid and flexible control over the progress of the fit. I-NoLLS is written in a modular way that allows the easy i ncorporation of new modules for calculating observable quantities from model parameters. The structure of the program allows straightforward parallelisation of the time-consuming property calculations. In pilot applications, I-NoLLS has been interfaced with programs for calculati ng bound states of Van der Waals complexes, cross sections for molecul ar scattering processes, and second virial coefficients of gas mixture s. Parallelisation of the property calculations has been achieved usin g PVM running on a cluster of workstations.