NL-FIT: a microcomputer program for non-linear fitting.

Abstract

A program for a microcomputer (HP 85) has been written using BASIC language. Given the analytical form of a model y: R leads to R the program computes the optimal parameters for non-linear least-squares fitting and gives information for its statistical evaluation. The program uses the Gauss-Newton algorithm with Marquardt's modification and other tricks. During the run a message is displayed if there is a high correlation between one or more couples of parameters to establish an interactive dialogue with the user on critical problems. The authors' aim was to make the program sufficiently quick and easy to use, efficient for a wide class of models and robust enough to deal with bad starting parameters.