Re: [igraph] leading.eigenvector.community function

[Szabolcs Horvát]

On 25 May 2017 at 19:43, Edmund Hunt <address@hidden> wrote:
> Hi Gabor,
>
> Thanks for your reply.
>
> Here are 4 different commands and their result, I guess I am just a bit
> confused how they relate to each other.
>
> The first two are using the cluster_leading_eigen alone, the second two use
> that command to find the communities and then the modularity function to get
> the modularity value out of it
>
> Would I be right in understanding that cluster_leading_eigen only uses the
> weights argument after the communities have been found - but then why does
> it return the same value below for the first two commands - and why is it
> different to the third command
>
> Thanks
>
>> cluster_leading_eigen(net, weights = E(net)$weight)
> IGRAPH clustering leading eigenvector, groups: 2, mod: 0.055
> + groups:
>   $`1`
>   [1] "YV" "B"  "P"
>
>
>
>   $`2`
>   [1] "DG" "V"
>
>
>> cluster_leading_eigen(net, weights = NULL)
> IGRAPH clustering leading eigenvector, groups: 2, mod: 0.055
> + groups:
>   $`1`
>   [1] "YV" "B"  "P"
>
>
>
>   $`2`
>   [1] "DG" "V"


According to the documentation, you need to supply weights=NA, and not
weights=NULL, to ignore any existing weight values in the graph.

>
>> modularity(net,membership(cluster_leading_eigen(net, weights =
>> E(net)$weight)),weights=NULL)
> [1] 0.03061224
>
>> modularity(net,membership(cluster_leading_eigen(net, weights =
>> E(net)$weight)),weights=E(net)$weight)
> [1] 0.0546875
>
>
>
> On 25 May 2017, at 06:51, Gábor Csárdi <address@hidden> wrote:
>
> IIRC the original algorithm can be extended easily to take weights
> into account.
>
> If you think the igraph is not doing that (and the docs say that it
> would), can you please provide a small example that gives you the same
> results with or without (large enough) weights? Thanks.
>
> Gabor
>
> On Wed, May 24, 2017 at 10:11 AM, Edmund Hunt <address@hidden> wrote:
>
> Hello,
>
> I have a question/comment about the leading.eigenvector.community function
> in igraph
>
> It has an argument for weights, but this seems to make no difference to the
> calculated clusters/resulting modularity
>
> Indeed I don’t think Newman’s algorithm takes edge weights into account?
>
> Is it the case that the weights are only used after the community detection
> has taken place, to calculate a modularity value? Is it appropriate to use
> the weights to calculate modularity, can anyone advise me what is the
> ‘right’ thing to do with a weighted, undirected network - is it definitely
> to use the weights in the modularity calculation, or is there a free choice
>
> Perhaps these issues could be made clearer in the function help
>
> Thanks
>
> _______________________________________________
> igraph-help mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/igraph-help
>
>
> _______________________________________________
> igraph-help mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/igraph-help
>
>
>
> _______________________________________________
> igraph-help mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/igraph-help
>