[igraph] community detection

[zhengjun chen]

Hi,

I use "fastgreedy" community detection algorithm to find community in my graph.

It detects two communities 1 and 2. Each community consists of some high-degree vertices. 

To some extent, the vertex's degree reflects the role of the vertex in its community. 
I look at these high-degree vertices, and meet a problem.

One vertex called A belongs to community 2. It has connections to two high-degree vertices B and C of community 2. But it also has connections to two high-degree vertices D and E of community 1. 

So, why vertex A is divided into community 2? I look at its neighbors.

It has about 30 common neighbors with vertices D and E, while only has 10 common neighbors with B and C.

It goes against my intuition that is vertices in the same community should share more neighbors.

So, I am wondering whether I get a wrong result of community division. Or any other explanation for my problem.

 

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Thanks
zhengjun