Hi everyone,
I want to calculate the betweenness of each node for a network with 13498 nodes
and 101565 edges.
by simply call betweenness(nodes,directed=False), it takes about 32 seconds on
my 8-core computer. That seems good.
However, I just considering use full of my CPU to accelerate it. So I use PPL,
which is a parallel library for C++ in VS2012, and I made following code:
igraph_vector_t test;
igraph_vector_init(&test, 0);
parallel_for(0,vcount-1,[&g,&test](igraph_integer_t i){
clock_t t1=clock();
igraph_betweenness(&g,&test,igraph_vss_1(i),IGRAPH_UNDIRECTED,0,1);
clock_t t2=clock();
cout<<i<<"\t"<<igraph_vector_e(&test,0)<<"\t"<<t2-t1<<endl;
});
finish=clock();
cout<<finish-start<<endl;
BUT! It is very slow! It takes about 2 minutes to calculate betweenesses of 7
nodes in parallel!
It is faster if I use:
parallel_for(0,vcount-1,10000,[&g,&test](igraph_integer_t i){
clock_t t1=clock();
igraph_betweenness(&g,&test,igraph_vss_seq(i,i+9999),IGRAPH_UNDIRECTED,0,1);
clock_t t2=clock();
cout<<i<<"\t"<<igraph_vector_e(&test,0)<<"\t"<<t2-t1<<endl;
});
It takes about 1 minute...
So why is it?
In my opinion, if we put many nodes into a same thread, they can share the
information of visited paths by other nodes. Am I right?
Has anybody tried parallel computing of igraph?
Gang_______________________________________________
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