Determines how arcs should be displayed
above_below(edgelist, above)two-column matrix
optional numeric or logical vector
indicating what edges (arcs) should be plotted above (or
to the right of) of chosen axis If above = NULL
then all arcs are plotted above (or to the right) If
above is numeric, it cannot contain both positive
and negative indices. If above is logical, its
length must equal the number of rows in edgelist
a logical vector indicating how arcs should be displayed
If horizontal = TRUE then arcs can be plotted
above or below the horizontal axis If
horizontal = FALSE then arcs can be plotted to the
right or left of the vertical axis