[igraph] What exactly does igraph_transitivity_undirected() compute for directed graphs?

[Szabolcs Horvát]

Hello,

What precisely does igraph_transitivity_undirected() compute for
directed graphs?

The C documentation states that

"Directed graphs are considered as undirected ones."

but this is not exactly the case.

With an example using the R interface (for simplicity),

> g<-make_graph(c(1,2, 2,1, 2,3, 3,1))
> transitivity(g,"local")
[1] 0.3333333 0.3333333 1.0000000

> transitivity(as.undirected(g),"local")
[1] 1 1 1

Can someone clarify what precisely is computed in the directed case?

Szabolcs