Hello,
In RooFit_Users_manual_2.07-29, I can not find Appendix C. where can I find it?
If I want to know the differences between the default fitting method in ROOT and in RooFit, whether I can get the answer from Appendix C?
Thanks
foolfish
Hello,
In RooFit_Users_manual_2.07-29, I can not find Appendix C. where can I find it?
If I want to know the differences between the default fitting method in ROOT and in RooFit, whether I can get the answer from Appendix C?
Thanks
foolfish
Hello,
The authors wrote in the Appendix C of the manual “This section is scheduled for the next version of the manual” (see page 69). I have pointed your post to Wouter Verkerke and I hope he will answer your question.
Cheers, Ilka
Hi,
Thanks for your helps!
foolfish
Hi,
Appending C is still work in progress (unfortunately).
Is there a specific question I can answer for you meanwhile?
Wouter
Hi, Wouter
I am sorry to reply later . I have two question:
Best regard!
foollish
Hi,
sorry for the late replay.
See for example section 32.1.2 and 32.1.3 in
pdg.lbl.gov/2004/reviews/statrpp.pdf
For a TGraph in general you should use the chi2 method and this is what is done in ROOT when fitting via TGraph::Fit.
In some special cases, for example when fitting efficiencies, which have the binomial errors, then it is recommended to use a log-likelihood method.
The weights used when fitting a TGraphErrors takes into account also the error on the x value (coordinate).
The effective variance method is used. The chi2 element are computed as
the sum of the quantity below at each point:
(y - f(x))**2
-----------------------------------
ey**2 + (ex*f'(x))**2
where ey is the error on the value y, ex is the error in x.
Best Regards
Lorenzo
Thanks for your reply!
foolfish