Minuit/Migrad Fitter

Newbie
1

Hello,
When I execute the command
fitr->Print();
ROOT prints the following statistics

MinFCN                   
Chi2                 
NDf                   
Edm                    
NCalls

What are MinFCN, Edm, and NCalls?

2

Hi,

  • MinFCN minimum value of the objective function used for fitting (chi2 for a least square fit or negative log-likelihood for a maximum likelihood fit)
  • Chi2 chi2 value obtained using the fitting funciton. It is equal to MinFCN when doing a least square fit.
  • NDf number of degree of freedom of the fit. Equal to Number of bins - number of fit parameters when fitting an histogram
  • Edm expected distance from the minimum. It is used to check if the found minimum is reliable. If
    it is not small (e.g. < 1.E-3) , it means your fit did not converge well.
  • NCalls number of time the objective function is called during minimization.
1 Like
3

Thank you!