Specifies a user-defined fit function.
Defines the function y = f(x) = p1 + p2 * x as the fit function.
Defines the function externally supplied in the executable myfct
as the fit function
Specifies the fit function. The parameter name is interpreted as follows.
First name is assumed to be an executable file which supplies an
externally defined fit function. If the file doesn't exist or isn't
executable then name is assumed to be a single line analytical expression.
Reserved identifier names for the fit parameters are p1,p2,p3,...,pn.
If this assumption fails also, the command wil be aborted.