[igraph] Any examples of "overlaid" graphs?

[Paul Johnson]

I'd like to make a drawing that has objects positioned with directed
arrows, and then load a new dataset that can be used to add "different
arrows" between the objects.  For example, I could draw a family tree
with fathers, mothers, and children,  and then "superimpose" a contact
network to show which agents talk to each other on the phone.

I've been using igraph's C library to do some analysis and generate
the edge file, and then I bring that into R for interactive analysis.
This works pretty well, although I've just scratched at the surface of
igraph's power so far.

I'm having a little trouble figuring out how to organize the data in
the edge files so that this will be possible to overlay the 2 sets of
edges.  Does anybody have a working example?

In the project, there are lots of networks, and I've been using
igraph's subgraph function to collect up a subset of 20  vertices for
illustration.  In tkplot, the vertex numbers are always re-assigned
from 1 to 20, and so I'm somewhat unsure about how to best create the
text file with the edges in it.

If you can advise me, I would appreciate it.

-- 
Paul E. Johnson
Professor, Political Science
1541 Lilac Lane, Room 504
University of Kansas