2PLOT: plot fit - perform a linear least-squares fit

Usage: plot fit <x> <y> <s> <f1>...

List mode:
The command performs a linear least-squares fit of the basis functions
given bythe vector expressions f1,... to the data points with x-coordinates,
y-coordinates and errors given by the vector expressions x, y and s,
respectively. For m basis functions, f1,...,fm the optimal linear combination,
is determined by minimizing the chi^2 value. The optimal fit function is
added as another column to the list data. This command does not draw
anything. The fit parameters, their standard deviations, and the
probability that this value of chi^2 would be exceeded by chance are
available through the intrinsic functions fitpar, fiterr, fitchisq
and fitprob, respectively. If the errors  of the data points are
unkown, this can be indicated by setting s to zero in the fit command.
