Re: [igraph] Obtaining communities and modularity index for an undirected graph

[Tamás Nepusz]

> All I've used so far is only "ready-made" implementations of the Girvan
> Neumann algorithm, and I don't remember having had to set the number of 
> steps. All I remember getting was one community assignment presented to 
> me as THE GN clustering for that undirected network.

The original publication of the Girvan-Newman algorithm (see 
http://www.pnas.org/content/99/12/7821, preprint: 
http://www.santafe.edu/media/workingpapers/01-12-077.pdf) does not describe how 
to select the number of communities (i.e. how to decide where to cut the 
dendrogram). As far as I know, most of the existing implementations use the 
modularity score or some other internal quality criterion to decide the number 
of communities. For instance, the SNAP library uses the maximum modularity 
criterion.

Cheers,
Tamas