whats the correct term for a "diamond" an directed acyclic graph?

Question

I want to talk about places in a directed acyclic graph where there is more than one path from node node to another. It's not a "cycle", what should I call it? I'm using the term "diamond", but that implies just four nodes, which is not right.

Answer 1

As you stated, the correct term is unlikely to be diamond graph, which already has a similar but slightly different meaning.

It's ugly, but the graph you're referring to is a homeomorphism of the dipole graph. That is, you can simplify the graph by contracting any edge with in- and out-degree 1.

From past experience, graph theoretic terminology can be tough. If you've got friends or colleagues who are mathematicians, they should always be your first port of call in such cases. If you've got time up your sleeve, you can use a good reference on graph theory. I recommend either Graph Theory by Bondy and Murty or Graph Theory by Diestel. If neither are available, you could always try wikipedia, or one of the math related stackexchange sites.