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Access/Evaluate Likelihood Function

Roofit and RooStats
#1

Hi everyone,

I have a question regarding directly accessing the likelihood function in RooFit. I currently have my p.d.fs as RooHistPdf objects and I then use this to fit to some binned dataset. Just for sanity check and out of curiosity, I want to manually fix the values of my parameters and see what value of the likelihood comes out. For example, I want to fix par_1= x and par_2 =y and see what value of FCN I get. In this case, no fitting is being done and is therefore independent of the actual dataset I end up fitting to. Is there a way to do this? Thanks!

#2

Hi! You are currently fitting with RooAbsPdf::fitTo(), right?

You can create the negative log-likelihood function in a similar way with RooAbsPdf::createNLL().

This will return you a RooAbsReal* for the NLL. For your sanity check, you need to set the values of all parameters manually with setVal(), and then you can evaluate the NLL with nll->getVal().

Please let me know if this works for you and if you have further questions!