X = userdata(Obj)
OBJ = userdata(Obj,X)
Obj [ model | tseries | VAR | SVAR | FAVAR ] - One of the IRIS objects with access to user data functions.
X [ ... ] - Any kind of data that will be attached to, and stored within, the object OBJ.
X [ ... ] - User data that are currently attached to the object.
Obj [ model | tseries | VAR | SVAR | FAVAR ] - The object with its user data updated.