This returns the parameters , state variables
# S3 method for RxODE
coef(object, ...)is an RxODE object
ignored arguments
a rxCoef object with the following
params is a list of strings for parameters for the RxODE object
state is a list of strings for the names of each state in
the RxODE object.
ini is the model specified default values for the
parameters.
RxODE is the referring RxODE object