Fit is a native view command added by Harold Levy, for fitting arbitrary nonlinear functions to data. Here is what is printed in view in response to "help" for fit.
fit < data > < function > < param1 > < param2 > ... Fit a computed function to a data curve with the same basis. This is done via simplex minimization of chi^2 over the specified parameters of the function. The constant "fit_tol" is used to specify the goodness of fit, and is created with a default value of 0.001 if not previously set. Output can be redirected to a specified file if the " > file_name" convention is appended to the command line.
Here is a simple example to type in to understand fit:
here is a simple example to type in to understand "fit" basis i = 1:100:1 ## make a straight line curve a = 10 ## make up some variables b = 100 ## make up some variables y == a*i + b ## set up a model equation for a straight line fplot y i ## note how parameter a and b are a bad fit to data i fit i y a b ## run the fit program fplot y i ## note the better fit
Here is a more intense example ...
basis v=0:5:1 ## independent variable i = 1.23e-6 * log(1+exp((v-.67)/.05))^2 ## here's the data i0 = 1 ## make up some variables vt = 1 ## make up some variables f == i0 * log(1+exp((v-vt)/.05))^2 ## here's the model fplot i f ## look at initial bad fit fit i f i0 vt ## fit with fit_tol = 1e-3 fplot i f ## look at better fit fit_tol = 1e-12 ## try for even better fit i f i0 vt ## fit with better guess style 1 circ ## here's new plot style fplot i@1 f ## look at best fit list i0 vt ## dump the values