Implement multigraphs

[alphajuliet]

Many useful graphs have multiple edges between vertices, although it can complicate some algorithms. The alternative is to manage multiple edges manually, for example storing a count property on an edge, or a list of named properties that represent each alternative instance of that edge.

See Ubergraph for an implementation example in Clojure that supports multigraphs with both directed and undirected edges.

[stchang]

Thanks for the reference. Definitely agree that multigraphs are good to have.