The MINUIT package acts on a multiparameter Fortran function to which one
must give the generic name FCN.
In the PAW/HBOOK implementation, the function FCN is called
HFCNH when the command Histo/Fit (PAW)
or the routine HFITH are invoked.
It is called HFCNV
when the command Vector/Fit or the routine HFITV are invoked.
The value of FCN will in general depend on one or more variable parameters.
To take a simple example, suppose the problem is to fit a polynomial through a set of data points with the command Vector/Fit. Routine HFCNV called by HFITV calculates the chisquare between a polynomial and the data; the variable parameters of HFCNV would be the coefficients of the polynomials. Routine HFITV will request MINUIT to minimize HFCNV with respect to the parameters, that is, find those values of the coefficients which give the lowest value of chisquare.