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Re: dual graph

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Mon, 26 Jun 2006 19:31:05 GMT
Message-ID: <ZBWng.2593$pu3.62899@ursa-nb00s0.nbnet.nb.ca>


Marshall wrote:

> Chris Smith wrote:
> 

>>David Cressey <dcressey_at_verizon.net> wrote:
>>
>>>Thanks to everybody for clearing up the matter of "planar".
>>>
>>>Now, I'm interested in a a subset of the planar graphs.
>>>
>>>It's the graphs that don't divide the space into more than one region.
>>>
>>>It seems to me that it's appropriate to call such graphs "hierarchical
>>>graphs", or simply "hierarchies". But I'm not sure. Can anyone clear this
>>>up?
>>
>>Well, such a graph has no cycles, so it is a forest. If it's connected,
>>then it's a tree.
> 
> I would have thought that to call an acyclic graph a tree, it would
> have to have a distinguished node. Yes? No? My answer to
> David's question would have been "acyclic." But again: not my field.

A DAG is acyclic and not every DAG is a tree. Is a DAG acyclic only in the sense that the edges are directed? And would not be acyclic if the edges were undirected? I think that makes sense to me. Received on Mon Jun 26 2006 - 14:31:05 CDT

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