dependence of results of fit with scaling

Hello,

here is a question raised on roottalk/stat and math tools, just in case somebody in this forum would know. thank you

i occur a strange behaviour with roofit. Let's start from a given TH1 HistoInitial, transformed to RooDataset via import function, then make a fit with a given model (with roofit). It gives result1 for the parameters of the fit

Let's now create a void TH2 HistoFinal, where we do something like HistoFinal.Add(HistoInitial, 1)
for a weight of 1, the fit of the HistoFinal gives the same results

But if one put a weight of 2 (for example), the results are a bit differents

Note that i reinitialized the parameters of the RooRealVar before doing each fit, in order to be in the same conditions.

I put a minimum example here :
/afs/cern.ch/user/e/escalier/public/MinimumProblem/

==>

root -b
.L MinimumProblem.C
MinimumProblem()
then just change the Add with 2 instead of 1 and you will see that the two fits (the initial one and the final one, don't give the same results)

Any suggestion is welcome

Thank you so much for your help Received on Sat Dec 25 2010 - 11:35:40 CET