This function creates a poset for use in a pim model based on a
number of observations and a comparison type. This function is
called from new.pim.poset and returns a list that
can be used as a value for its argument compare.
Usage
create.poset(compare = c("unique", "all"), n)
Value
A named list with 2 elements, called "L" and "R", containing
the selection indices for the left hand and right hand side of a pim.
Arguments
compare
a character value, either 'unique' or 'all'
n
an single integer value indicating how many observations there
are in the model.