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## [igraph] Re: igraph

 From: Agustin Lobo Subject: [igraph] Re: igraph Date: Mon, 03 Nov 2008 18:31:20 +0100 User-agent: Thunderbird 2.0.0.17 (X11/20080925)

```Thanks,

do the weights have to fulfill any particular
requirement for each method?

Agus

Gábor Csárdi wrote:
```
```Dear Agus,

currently the following community detection algorithms are implemented
in igraph:

fastgreedy.community
walktrap.community
spinglass.community
edge.betweenness.community

Please see their manual pages for references.

communities themselves, the other three methods return dendrograms,
you need to cut these to get the actual communities. A fairly standard
way is to cut at the highest modularity value, the modularity values
are returned by the fastgreedy and the walktrap methods (if you give
the modularity=TRUE argument). For the edge betweenness based method
you have calculate them by calling 'modularity'. See the example at
http://igraph.sf.net -> Screenshots -> Creating animations.

These methods use different heuristics to maximize modularity, if you
get consistent results with the different methods that is a good sign.

Btw. these questions are more suited to the igraph-help mailing list,
see http://igraph.sf.net -> Community -> igraph-help

Best Regards,
Gabor

On Mon, Nov 3, 2008 at 2:44 PM, Agustin Lobo <address@hidden> wrote:
```
```Dear Gabor Csardi,

I've been trying your R package igraph, but feel a bit
lost in the methods, so I'm taking the liberty of
I have a matrix of transportation (nb of trips, T) among cities. I've
defined

t(i,j) = T(i,j)/sum(t(i,.)

Then I've created a graph with:

My goal is to find communities defined by those cities that most interact.
I've tried
g3w <- walktrap.community(g3)
community.to.membership(g3, g3w\$merges, steps=9)

but I'm not really understanding what I'm doing. Could you point me
to some references and/or advice on which method would be best suited for my
goal?

Thanks!

Agus

--
Dr. Agustin Lobo
Institut de Ciencies de la Terra "Jaume Almera" (CSIC)
LLuis Sole Sabaris s/n
08028 Barcelona
Spain
Tel. 34 934095410
Fax. 34 934110012
http://www.ija.csic.es/gt/obster

```
```

```
```
--
Dr. Agustin Lobo
Institut de Ciencies de la Terra "Jaume Almera" (CSIC)
LLuis Sole Sabaris s/n
08028 Barcelona
Spain
Tel. 34 934095410
Fax. 34 934110012