Re: [igraph] Community in networks with many nodes but low link-density

[Charles Novaes de Santana]

Hi Gábor, thanks for your answer,


>> I am trying to study the modularity of networks with many nodes but
>> low link-density (48082 nodes and 12869 edges). I tried to use
>> walktrap.community and fastgreedy.community functions, but those
>> methods didn't work (segmentation fault).
>
> really? They might give an error, but they should not segfault. Which
> version of igraph is this?

Yes, I thought this segfault was due to a resource limitation of my
machine (a pc with 4Gb of RAM). I am using igraph-0.6 and that was the
message I got:

> net<-read.graph("./network.net",format="pajek")
> comm<-fastgreedy.community(net)

 *** caught segfault ***
address (nil), cause 'memory not mapped'

Traceback:
 1: .Call("R_igraph_community_fastgreedy", graph, as.logical(merges),
   as.logical(modularity), as.logical(membership), weights,
PACKAGE = "igraph")
 2: fastgreedy.community(net1)
aborting ...
Segmentation fault (core dumped)

>
> I would check the fastgreedy and the spinglass algorithms, these tend
> to give better results in terms of modularity (if that's what you are
> going for), with the newest version of igraph (0.6.x).
>
> Maybe it would be better to extract the connected components from your
> graph, and run the algorithm(s) of them. It does not really make sense
> to run community detection on a disconnected graphs, at least not the
> algorithms that are currently implemented in igraph.

Hmmm thanks for the suggestion, I tried again using only the connected
components from my networks and the fastgreedy.community worked fine!
Thank you very much!

Best,

Charles

>
> Best,
> Gabor
>
>> Thanks in advance for any help.
>>
>> Best,
>>
>> Charles
>>
>> --
>> Um axé! :)
>>
>> --
>> Charles Novaes de Santana
>> http://www.imedea.uib-csic.es/~charles
>> PhD student - Global Change
>> Laboratorio Internacional de Cambio Global
>> Department of Global Change Research
>> Instituto Mediterráneo de Estudios Avanzados(CSIC/UIB)
>> Calle Miquel Marques 21, 07190
>> Esporles - Islas Baleares - España
>>
>> Office phone - +34 971 610 896
>> Cell phone - +34 660 207 940
>>
>> _______________________________________________
>> igraph-help mailing list
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>
>
>
> --
> Gabor Csardi <address@hidden>     MTA KFKI RMKI
>
> _______________________________________________
> igraph-help mailing list
> address@hidden
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-- 
Um axé! :)

--
Charles Novaes de Santana
http://www.imedea.uib-csic.es/~charles
PhD student - Global Change
Laboratorio Internacional de Cambio Global
Department of Global Change Research
Instituto Mediterráneo de Estudios Avanzados(CSIC/UIB)
Calle Miquel Marques 21, 07190
Esporles - Islas Baleares - España

Office phone - +34 971 610 896
Cell phone - +34 660 207 940