Fix the dyads in fixed.dyads at their current value, preserve the edges in present, and preclude the edges in absent.
# fixedas(fixed.dyads, present, absent)a two-column edge list or a network
present and absent differ from fixed.dyads in that
they check that the specified edges are in fact present and/or
absent and stop with an error if not.
ergmConstraint for index of constraints and hints currently visible to the package.
ergm:::.formatTermKeywords("ergmConstraint", "fixedas", "subsection")