Internal and external constraint

Roofit and RooStats
1

Hi All,

I have a question regarding internal and external constraint. I know how to use them in my code and used both of them and the result is almost the same. So I am wondering What exactly they do into likelihood function?

Thanks in advance.
Maryam

2

Hi,

I am not sure what exactly you mean with internal and external constraints. Assuming you are referring to the definitions in tutorial rofit/rf604_constraints.C.
In this example, internal means that the model pdf contains a constraint term. For example your model is a
Poisson(n | s+b) Gaussian(b, b0, sigma_b). Now the Gaussian is a constraint for b.
External means that the constraint function is not in the current model you are fitting, but the user supplies this additional function externally using the command ExternalConstraint.
The result at the end should be the same if you are using the same functions

Lorenzo