The fit is executed by the command FIT.
Weighting factors for the data are chosen according to the choices made with the command FERROR.
If no errors are given an estimate will be made so that the chi-square
corresponds approximately to 1.
Note that the fit may be very sensitive to the choice of appropriate weighting factors.
Data less or equal zero are excluded from fit by default but may be demanded to be considered.
The execution of a fit is stopped when convergence is reached, by a maximum
number of iterations or by exceeding a CPU-time limit; it may of course
be restarted with the actual fit parameter set. In case of critical fit
conditions some internal parameters may be altered by means of the command FMLFIT.