Each instance of setup_Lpar.* calls a function create_Lpar_* that
creates an object Lpar.
It is attached the xds object as pars$Lpar[[s]]. Each instance of create_Lpar_*
should assign default parameter values that will be over-written by Lopts
setup_Lpar(Lname, pars, s, Lopts = list())the class name of the aquatic model
an xds object
the species index
a named list to configure Lpar
an xds object
This method assigns Lname to class(Lname) and dispatches on Lname.