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
