Re: [igraph] A question about Greedy community algorithm

[Tamas Nepusz]

> After performing Community detection the resulting Dendogram
> contains merges such as
>  (4834, 12676),
>  (5036, 12677),
>  (3744, 12329),
> When there are only 12575
> nodes.
> what do 12677 these numbers indicate?
Let us assume that you have n nodes in your graph. This means that  
node indices go from 0 to n-1. Let us assume that you merge nodes i  
and j in the first step. When you merge them, the "virtual" node in  
which they got merged gets the next available node index; that is,  
index n. When you merge the next two nodes, the merged node becomes  
node #n+1, and so on. This is how you can get node indices larger than  
n. Or, in other words, as the documentation for the R package says:

"Each line is one merge and it is given by the ids of the two  
communities merged. The community ids are integer numbers starting  
from zero and the communities between zero and the number of vertices  
(N) minus one belong to individual vertices. The first line of the  
matrix gives the first merge, this merge creates community N, the  
number of vertices, the second merge creates community N+1, etc."

--
Tamas