Minos option for "fitTo"

Dear RooFit experts,
I see from the RooFit user guide that for the “fitTo” method the “Minos(Bool_t flag) : Flag controls if MINOS is run after HESSE, on by default”.
If I call “fitTo” in the following way:
(A) TotalPDF->fitTo(*dataSet)
and in the following way:
(B) TotalPDF->fitTo(*dataSet,Minos(true))

(B) takes way longer to run with respect to (A) !!!
So my question is, is Minos really ON by default ?
If yes, why there is such a difference between (A) and (B) in terms of running time ?


  • Mauro.


Minos is not run by default and it is normal that it takes much longer. Running Minos requires several minimization in (n-1) dimension for each parameter.
See seal.web.cern.ch/seal/documents/ … nerror.pdf