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Re: [igraph] community detection

From: Tamas Nepusz
Subject: Re: [igraph] community detection
Date: Wed, 10 Feb 2010 19:19:36 +0000

> Then I use igraph_community_to_membership () to create a membership vector 
> from a community structure dendrogram. My question is how to fill the 
> parameter steps in this function. Right now I use the value corresponding 
> largest modularity. 
That's what I would do as well. Actually, that's also exactly what the Python 
interface does.

> I find that there are several largest modularity values in my case. In other 
> words, several steps have the same modularity. They do not have the same 
> resulting membership. So, which steps I should choose?
Whichever you want ;) I'd choose either the smallest or the largest. Note that 
if you are working with the fast greedy algorithm, the modularity values that 
are equal to each other should happen at consecutive numbers of steps due to 
how the algorithm works. (I.e. it can be shown that once the modularity started 
to decrease after a merge, it will keep on decreasing until it eventually 
reaches zero).


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