> > It seems that log-likelihood fitting is integerizing bin > > contents before fitting. Is this intended behavior? Hi Burt, likelyhood fitting is based on known function of distribution. In current case it is binomila or poisson. It supposed that bins contain number of entries. So they should be integers. If you use weighted histogramm, then distribution of sum of weights in bin is not poisson, and anyway result of fit is wrong. Victor Dave Morrison wrote: > > Hi Burt, > > Yep. This has been a topic of discussion in PHENIX computing recently. > Here are the lines that do the deed (H_H1.cxx:1546-1550): > > if (fu < 1.e-9) fu = 1.e-9; > icu = Int_t(cu); > fsub = -fu + cu * TMath::Log(fu); > fobs = hFitter->GetSumLog(icu); > > The bin contents are floor()'ed. I suppose one could argue that since > the log likelihood procedure in TH1::Fit happens to assume a poisson > probability for sampling the observed bin contents from the model you're > on somewhat sketchy ground if the bins don't contain integer values, but > I think the last line above should be changed to > > fobs = hFitter->GetSumLog(cu); > > if only to avoid needless surprises. > > Cheers, > Dave > > Burt Holzman wrote: > > > It seems that log-likelihood fitting is integerizing bin > > contents before fitting. Is this intended behavior? > > -- > David Morrison Brookhaven National Laboratory phone: 631-344-5840 > Physics Department, Bldg 510 C fax: 631-344-3253 > Upton, NY 11973-5000 email: dave@bnl.gov -- Victor M. Perevoztchikov perev@bnl.gov perev@vxcern.cern.ch Brookhaven National Laboratory MS 510A PO Box 5000 Upton NY 11973-5000 tel office : 631-344-7894; fax 631-344-4206; home 631-345-2690
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