[igraph] Calculating weighted betweeness ? Missing something in documentation ?

[address@hidden]

Hi,

I was trying out the development version 0.6 from http://code.google.com/p/igraph/downloads/list

How is actually weighted betweenness implemented ? I would like to know what I am calculating, and its not in the documentation.
How weights are used ? 

To my knownledge there is a paper "Node centrality in weighted networks: Generalizing degree and shortest paths" by Tore Opsahl et al. Social Networks 32 (2010) 245–251, explaining how weighted betweenness can be calculated with a tuning parameter alpha, giving more important either to path length or to weights. 

How is that implemented in R ? Is that the same measure that is implemented in igraph ? 

Thanks