Re: [igraph] fastgreedy.community fails on Zachary karate club data set

[Arun]

As the error message says, the FastGreedy algorithm only works on
simple graphs (i.e. graphs with no self-loops or multi-edges).  Your
version of the Karate graph most likely has duplicate edges or
self-loops.

The Karate network available from Mark Newman's website
(http://www-personal.umich.edu/~mejn/netdata/), has only 78 edges, I
think.  From your output, however,  your Karate network has 154 edges.
 Check your data and remove self-loops and duplicate edges.   Fast
greedy should work after that.  Also, see the igraph.Graph.simplify()
method if you want to simplify quickly and avoid editing the
underlying dataset.




On Tue, Jan 25, 2011 at 7:23 PM, Liang Wang <address@hidden> wrote:
> Hi,
>
> When I ran fastgreedy.community algorithm on the Karate data set,  I got an
> error message, as shown below. What am I doing wrong here?
>
> Thanks a lot for your help.
> Liang
>
>> G  <- read.graph('./krate0.txt',format="edgelist",directed="FALSE")
>> G
> Vertices: 34
> Edges: 154
> Directed: FALSE
> Edges:
> [0]    0 --  1
> [1]    0 --  2
> [2]    0 --  3
> [3]    0 --  4
> ....
> [150] 29 -- 33
> [151] 30 -- 33
> [152] 31 -- 33
> [153] 32 -- 33
>
>> fc <- fastgreedy.community(G)
> Error in fastgreedy.community(G) :
>   At fast_community.c:540 : fast-greedy community finding works only on
> simple graphs, Invalid value
>
>
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