[Nauty-list] amtog and digraphs

Gordon Royle gordon at maths.uwa.edu.au
Sun Aug 16 18:30:04 EST 2009

On 15/08/2009, at 3:32 AM, Eggermont, C.E.J. wrote:

> Hello,
> I'm very new to nauty.
> I want to remove isomorphs from a (smallish for now) list of 525  
> (small) digraphs.
> Since shortg only mentions undirected graphs I used
>  ./amtog -s list-of-digraphs | ./labelg | sort | uniq
> However I get a lot of warnings that the matrices are unsymmetric  
> (obviously).

The simple answer is that you are using programs and formats for  
graphs that do not support digraphs.

In particular, neither graph6 nor sparse6 format supports directed  

Note that nauty itself can canonically label directed graphs, but you  
will need to use a custom-made input/output routine...

> To test this it seems something goes wrong since
> running one of graphs of the output through ./showg
> gives a undirected (or multi-)graph!?
> Is there a good/better way to do this?
> Thanks for any assistance,
> Christian
> -o00o-o00-
> C.E.J.Eggermont at tue.nl
> http://www.win.tue.nl/~ceggermo/
> http://www.puzzled.nl/
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Prof Gordon Royle
gordon at maths.uwa.edu.au
School of Mathematics & Statistics
University of Western Australia

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