[RooFit] model with constraint, likelihood vs parameters


I am having difficulties in finding the dependence of likelihood on model parameters.

The PDF has one observable and 2 parameters. One of the parameters is constrained using conditional PDF. The model is fit do data and I would like to study the dependence of -ln(L) on parameters. The fit gives reasonable results however the plots of -ln(L) vs parameters contradict the fit. The plot of various distributions are attached together with essential parts of the code. The last pad shows RooMinuit contour plot, which contradicts -ln(L) vs mu dependence shown on the first pad. The third pad show -ln(L) vs both parameter with no minimum corresponding to contour plot. The likelihood calculated “manually” shows maximum, however createHistogram does not work and contains -NAN. RooFitResult::numInvalidNLL() returns 0. Would be great if an expert could help solving this issues.

tmp.C (3.53 KB)

Hi Margar,

Can you please post also the data set to be able to look into your problem ? I would like to see also the third plot
made as a contour plot. If you are fitting only two parameters should agree with the contour obtain by Minuit.


Hi Lorenzo

the attached ROOT file contains RooWorkspace and the data has name dataST.

I have to tell that I did some toy MC studies and now have doubts about the PDF itself. It seems the combination of RooExtendPdf and RooProdPdf with conditional normalization parameter does not work as I was expecting.

model.root (16.7 KB)