"ExternalConstraints(...)" for "createNLL"

Dear Experts,
what’s the meaning of the option "ExternalConstraints(…)"
for the member function: “createNLL” of the class RooAbsPdf ?

Let’s say I have p.d.f. and an “ExternalConstraint”

  1. I perform a fit
  2. I would like to know the value of the NLL at the minimum
    why the “ExternalConstraints(…)” should matter when I compute the value of the NLL ?

Thanks for the clarification.

  • Mauro.

See the example
root.cern.ch/root/html/tutorials … nts.C.html

for how the constraints are used in RooFit

Best Regards


Hi Lorenzo,
thanks for your answer.

I think I know how to use constraints for the “fitTo” member function.

What I was asking is why shall I need to specify the constraints in the “createNLL” member function.
In the example you pointed me to, there is no use of “createNLL”.


  • Mauro.


fitTo calls createNLL with the same options and then just minimize in addition the created nLL.