Dear experts,

I created a TF1 with a my (complicated) function, as described in section
" Creating a TF1 with a User Function" here:

Then I configured the Fit with initial values and I fixed two of them:

tf1->SetParameters(pow(10, 6), 100., 0.01, 0.23, 0.23, mass, Bratio);
tf1->FixParameter(5, mass);
tf1->FixParameter(6, Bratio);

at this point I implemented the Fit with the “FRV” options, on a TH1F histogram:

TFitResultPtr fitRes = th1f->Fit("tf1_name", "FRV");

and I obtained the following fit result that seems very good:

however the fit results with very high errors on the parameters, showin the following results (STATUS= NOT POSDEF):
(the full Fit results is here: NEW_S1_rootForum.txt (8.5 KB) )

Can i still accept the result (also if the very high errors)? What should I do to improve the Fit?
I would be very gratefull forn any kind of help.

Thank you a lot

I think @moneta can help

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