Explanation of createNLL

Dear RooFit experts,
I have a naive simple question,
I would like to understand a bit better what the member function “createNLL”, of the class “RooAbsPdf”, does:
on the documentation it is written that it computes: -log(L)
so I wonder why do I get negative values from myPDF->createNLL(…)->getVal()

L should be between 0 and 1
log(L) should be between -infinite and 0
-log(L) should be between +infinite and 0
So, if what I said is correct I should get positive values

Can you please explain a bit what exactly does createNLL ?

  • Mauro.
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