Re: graphs



> Oscar,
>
> > Have you chosen a graph data structure yet?  I assume you will use some
> > kind of adjacency list representation to support sparse directed graphs,
>
> I am currently testing with hand-made *positional* data, and do not have an
> underlying graph structure yet. I feel that the underlying structure in any
> case will go thru a heavy adaption process to visad math and display types,
> so this is not a problem.
>
> > but I am curious if you have chosen the data types for the node and edge
> > labels,
>
> If you are talking about a visad MathType structure for them, no. I have
> tried out two today, but both had problems. If you have suggestions, let me
> know.
>
> > and if you will be using primitives or objects.
>
> What primitives and objects do you mean?
>
> Manuel

Most of the graphs I work with are sparse enough to be most effeciently
represented as time varying vertex/edge lists....   I have considered using
irregular grids to represent these intrinsically to Visad.  While ultimately I
want to render nodes and edges, I also want to be able to take advantage of
interpolation off the graph to define continuous fields, etc.

Some of the graphs (especially if I take them over time) are dense enough to
suggest connectivity matrix representations and especially if I use a "sparse
matrix" package.  Does anyone here have anything to suggest in that realm?

I'll try to remember to report when I find good graph layout algorithms
implemented in Java that might be a good addition or complement to Visad.

I'm looking at openmap (www.openmap.org) for the geospatially referenced aspect
of my problem but haven't had much time yet.  My current work is taking a twist
toward focusing on internet infrastructure more than transportation and energy
distribution networks so the cybergeography folke (www.cybergeography.org) are
most interesting at the moment.

CAIDA (www.caida.org) has built an interesting layout/manipulation tool known
as Walrus (www.caida.org/tools/visualization/walrus) which implements a 3D
hyperbolic metric for layout and investigation which maintains excellent
scaling properties.  The early work was by Tamara Munzner but this is the best
example to date, that I know of  for handling the "detail in context" problem
around graphs.

It is also a Java App and I imagine they are likely to be cooperative if
someone wanted to "marry" this capability with Visad in an interesting way.

If all goes well, I may have the suite of INCCA graph analysis algorithms to
make available to this community but first I need to understand how best to
relate them to the Visad data structures.

It seems possible that we need a whole new base data structure that is parallel
to the ones already in Visad along with some conversion methods...    it might
be too wishful thinking to imagine that what are essentially point sets or
continuous fields in visad are close enough to graphs to be appropriate for the
kinds of manipulations done by graph theoretic algorithms.

- Steve