No differences. the gMinuit pointer is automatically set by teh
TMinuit constructor.
> I have another question: what to do, if I want to fix (not optimize at all)
> some parameters in TGraph::Fit ? I have quite good starting values for them.
> Before I run TGraph::Fit, I may not use gMinuit->mnfixp and then
> gMinuit->mnfree (or may I?). After I run TGraph::Fit all my parameters are
> changed.
Did you try the "B" option (Bound parameters). With this option,
you must specify the limits for your parameters. To freeze one
parameter, simply set the lower limit= the upper limit.
>
> I would suggest to add some "I" - init only option to ::Fit() - it would
> perform everything without calling gMinuit->mnmigr() and printing statistics.
> Then I have the gMinuit ready to run, but I can fine tune some parameters and
> run it then.
>
This option could be added, but I do not understand what you want
to do with TGraph::Fit in this case.
Rene Brun