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## [igraph] help need for the fast community detection algorithm

 From: Xing Jiang Subject: [igraph] help need for the fast community detection algorithm Date: Thu, 26 Jul 2007 16:06:58 +0800

Hi All,

I am now using igraph for community structure detection. I write a very simple program to call the igraph library. I want to see what the result is on the club graph shown in the example. However, I see this algorithm does not work and no partition performed.

the graph I want to test have 8 edges.Its structure  is like

1                 5
0          3 ------4       7
2                  6

node {0, 1, 2,3} & {4,5,6,7} are two cliques.

It is supposed to have two sub structures detected. However, I do not obtain such results. I test on NewMan's code. it works. But igraph does not work.

the following code is the one i use:

int main(void){
igraph_real_t modularity;
igraph_integer_t vertexNumber = 8;
igraph_integer_t edgeNumber = 13;

igraph_vector_t edges;
igraph_vector_t type;

igraph_t graph;

igraph_empty(&graph, vertexNumber, IGRAPH_UNDIRECTED);

igraph_vector_init(&edges, edgeNumber*2);

VECTOR(edges)[0]=0;
VECTOR(edges)[1]=1;
VECTOR(edges)[2]=0;
VECTOR(edges)[3]=2;
VECTOR(edges)[4]=0;
VECTOR(edges)[5]=3;
VECTOR(edges)[6]=1;
VECTOR(edges)[7]=2;
VECTOR(edges)[8]=1;
VECTOR(edges)[9]=3;
VECTOR(edges)[10]=2;
VECTOR(edges)[11]=3;
VECTOR(edges)[12]=2;
VECTOR(edges)[13]=4;
VECTOR(edges)[14]=4;
VECTOR(edges)[15]=5;
VECTOR(edges)[16]=4;
VECTOR(edges)[17]=6;
VECTOR(edges)[18]=4;
VECTOR(edges)[19]=7;
VECTOR(edges)[20]=5;
VECTOR(edges)[21]=6;
VECTOR(edges)[22]=5;
VECTOR(edges)[23]=7;
VECTOR(edges)[24]=6;
VECTOR(edges)[25]=7;

igraph_vector_init(&type,vertexNumber);

igraph_modularity(&graph,&type, &modularity);

igraph_integer_t zz = igraph_ecount(&graph);

printf("edge: %d\n",(int)zz);

printf("Modularity: %f\n",(double)modularity);

igraph_vector_destroy(&edges);
igraph_vector_destroy(&type);
igraph_destroy(&graph);

return 0;

}

--
regards
Jiang Xing