Extended Multidimensional Fit using RooFit


I am trying to fit data to a multidimensional model that is the product of two extended likelihood models. However, when I run the code model.fitTo(*data, Extended()), the system tells me that my model cannot take the extended fit option. I read that RooProdPdf can take the extended option if only one of the the models being multiplied is an extended likelihood model. Is there a way to get around this? How do I perform an extended likelihood fit on a model that is the product of two extended likelihood models using RooFit?



The issues is indeed that you have two 1-dimensional pdfs that each have an extended term.

You can of course trivially multiply these intro a two-dimensional pdf, however a 2D pdf can only
have one extended term. So if exactly one input of RooProdPdf provides an extended term, that
one is automatically taken as the extended term. If there is more than one, there is no automatic
solution to the problem and RooFit gives an error.

Do you know which one of the extended terms you would like to use for the 2D pdf?