I fit a 1D histogram with binning likelihood method (option “L”). Everything is OK before I want to extract the loglikelihood value. The method itself uses the function “FitUtil::EvaluatePoissonLogL” (see http://root.cern.ch/root/html/TH1.html) and the FCN is -loglike. In order to get the mimimun value of FCN, I use the code like “gMinuit -> fAmin”. A message (see http://root.cern.ch/root/roottalk/roottalk00/1963.html) said it gave “-2*loglike”). So the problems are
- Is FCN -log(L) or -2*log(L)
- Question 1) is connected with the error estimation, as for -log(L), the SetErrorDef should be 0.5, while 1 for -2*log(L).
- fAmin gives “-2*log(L)” or not?
Could anyone help me?