Re: [igraph] community detection

[Gábor Csárdi]

On Wed, Feb 10, 2010 at 9:48 PM, zhengjun chen <address@hidden> wrote:
> Thanks. Another question is how the community is indexed?

Arbitrarily.

Gabor

> That is, we say
> some vertices are in community 0, others are community 1. What is the order
> of community index? In other words, why this cluster is called community 0,
> and the other is called community 1?
>
> On Wed, Feb 10, 2010 at 2:19 PM, Tamas Nepusz <address@hidden> wrote:
>>
>> > 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).
>>
>> --
>> Tamas
>>
>>
>>
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>
>
>
> --
> Thanks
> zhengjun
>
> Graduate research assistant
> Dept of Computer Science and Engineering
> Lehigh University
>
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>



-- 
Gabor Csardi <address@hidden>     UNIL DGM