iMesh telecon: closure and adjacency

[James Porter]

On Tue, 2010-09-07 at 12:18 -0700, Carl Ollivier-Gooch wrote:
> One issue that was raised (more or less as an aside while talking about 
> iMesh compliance) is whether an entity should be considered adjacent to 
> itself.  The spec currently says that it is not, for first adjacencies. 
>   Also, the spec says that a second adjacency call should not return the 
> originating entity, even if it otherwise would.

In my experience, I've never found it useful to exclude an entity from
its adjacency list. While I understand the reasoning that "adjacent"
implies "not myself", it always just makes things harder for me. For
example, if I wanted to get all the information necessary to (re)create
a set of entities, I could use iMesh_getAdjEntIndices to get all the
entities plus the vertices that comprise them. However, this fails if
the set contains vertices too. I'm not sure if it's MOAB-specific or
not, but (as I recall) trying this even returns an error, so I don't get
*any* useful data.

At the very least, I think getting the adjacent vertices to a vertex
should just return an empty list instead of returning an error. There's
nothing so fundamentally "wrong" about returning same-dimension
adjacencies that it should return an error, in my opinion.

- Jim