Internal /External constraints in a fit


I would like to know what is the difference between applying an internal constraint to a parameter of a fit with respect to applying an external constraint ? In which case should we use one or the other ?

Thanks a lot for helping,


It’s up to you. It mostly matters when your p.d.f. is constructed and used in separate
pieces of code.

Internal constraints can be associated with a p.d.f. at the time when the
p.d.f. is constructed, which is sometimes convenient (usually when it is a 'standard’
constraint that you would often or always apply). External constraints need to
be constructed at the time you do the fit, which give you maximal flexibility.