Nonlin allows you to perform statistical regression analyses to estimate the values of parameters for linear, multivariate, polynomial, and general nonlinear functions. The regression analysis determines the values of the parameters which cause the function to best fit the observed data that you provide. Nonlin allows you to specify the form of the function whose parameters are being estimated using ordinary algebraic notation. In addition to determining the parameter estimates, Nonlin can be directed to generate an output file with predicted values and residuals. It can also plot the observed values and the estimated function and the residual values. In addition to performing regression analysis, Nonlin can also be used to find the root (zero value point) or minimum absolute value of a nonlinear expression.

The nonlinear regression algorithm used by Nonlin was published in ACM Transactions on Mathematical Software 7,3 (Sept. 1981) "Dennis, J.E., Gay, D.M., and Welsch, R.E. -- An adaptive nonlinear least-squares algorithm."

Nonlin is a "shareware" product.

Look at the readme file from the program.