Re: [jgrapht-developers] dumping adjacency and laplacian matrices

[Charles F. <cf...@us...>]

> MatrixExporter sounds good.  A pattern you might consider instead of
> static methods is to support "knob" methods for tweaking the formatting
> before the export, e.g.

Excelent.

Now that I'm getting a little deeper into this, I realized that a
Laplacian matrix is only defined for "an undirected, unweighted graph
without graph loops (i,i) or multiple edges from one node to another [1]."

   1. http://mathworld.wolfram.com/LaplacianMatrix.html

Currently there are interfaces for Directed and Undirected graphs, but
no interfaces are used to mark Multigraphs or Pseudographs. It is thus
impossible for me to tell beforehand whether or not the graph provided
contains loops or multiple edges.

The possible solutions that I see to this are to:

 - Define interfaces that indicate when multiple edges or loops are
   permitted in a graph, and explicitely check those, possibly issuing a
   warning.

 - Ignore loops, and collapse multiple edges when creating the Laplacian
   matrix.

I don't see any reason not to do the latter, although the former may
still be beneficial for other reasons.

Thoughts?

Charles

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