[igraph] Help with using igraph_centralization_betweenness

[Giuseppe G.]

Hi,

I have an undirected network of 3693 nodes and 9689 edges. The network 
has no self-edges and no multiple edges between any two nodes, and is 
connected.

I'm trying to obtain some global network statistics using the C igraph 
library. So far I have obtained the network diameter, the average path 
length, the global transitivity and the average of the local transitivities.

I would like a global measure summarising the node betweenness 
centrality for the network. I found this new method, 
igraph_centralization_betweenness, which sounds like what I need. 
However I'd like to be sure I'm using it correctly, because I'm getting 
surprising values. This is how I'm using the function

//etc..
FILE *instream;
igraph_t graph;
igraph_real_t centr_betw;
igraph_read_graph_edgelist(&graph, instream, 0, IGRAPH_UNDIRECTED);

igraph_centralization_betweenness(&graph,0, 0, 0,&centr_betw,&t_max,0);
printf("Betweenness Centralization %f, max %f\n", centr_betw, t_max);

which gives

Betweenness Centralization 4555078098.244157, max -980219902.000000

If I normalise the centralisation value, I'll get -4.646996

However I'm not sure these results are correct. The docs says the 
normalised betw.centralisation is a value between 0 and 1. Also, I have 
problems with the other two centralisation functions, eg doing

igraph_centralization_closeness(&graph,0, 0,&centr_clos,0,0);

yields

Error at centrality.c:2563 :calculating closeness, Invalid mode

and

igraph_centralization_degree(&graph,0, 0, 1,&centr_degree,0,0);

yields

Error at type_indexededgelist.c:941 :degree calculation failed, Invalid mode

What am I doing wrong? Thanks!

Giuseppe

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