[Nauty-list] Digraphs

[Mathieu Dutour]

On Sun, Jul 31, 2011 at 09:55:25AM -0400, Sterten at aol.com wrote:
>> when was he in Canada ?
CRM conference on polyhedral computations, Montreal, Canada, 23-26.10.2006

>> I vaguely remember that we discussed it here and it was improved (?)
>> maybe 2003 or 2005 ?
>>  
>> also, why do you need the sink/source - there should be a better
>> way to convert it into an undirected graph.
>> You won't even need colors. I should have a program, but forgot ...
Sorry, I did not explained myself correctly. For some cases like set systems
(say S1={1,2,3}, S2={2,3,4}), it is useful to have graphs having vertices
corresponding to vertices (1,2,3,4 here) and vertices corresponding to
sets (S1, S2 here) and the adjacency corresponding to incidence.
In order to avoid mixing up of vertices and sets one way (inefficient)
is to use oriented edges and another one (more efficient) is to use vertex
colors.

What I meant to say is that in my case it is not obvious how to do such a
reduction.

>> a simple executable that converts a digraph into an undirected graph
>> with same automorphism group ?!
That would be very nice. Even nicer would be to explain it with words to
me. Maybe it is very obvious and I did not thought enough.

  Mathieu