Re: [igraph] betweenness centrality -- negative and floating values?

[Yong Zou]

Thanks Tamas,

Now it is clear for those floating values. But what about the very big
or even negative values, then?

Best,
Yong

On Thu, May 28, 2009 at 1:33 PM, Tamas Nepusz <address@hidden> wrote:
>> Ok, I can understand the floating values for the BC then because of
>> this weight of 1/k. It also means that the more shortest paths between
>> A and B, the less weight will be counted.
>>
>> However from the original definition for BC,
>> http://en.wikipedia.org/wiki/Centrality, this sounds to be different
>> for me.
>
> No, it isn't. The formula on that Wikipedia page has the number of shortest
> paths between s and t in the denumerator, so if there is more than a single
> shortest path between s and t, the vertices participating in those paths
> will receive a contribution of 1/k due to this path, where k is \sigma_{s,t}
> - the number of shortest paths between s and t.
>
>> I'm quite confused by this now. The values should be
>> normalized to the interval [0 1]?
>
> It can be normalized if you wish, but igraph doesn't do that by default. As
> it says on the Wikipedia page you mentioned, "This may be normalised by
> dividing through the number of pairs of vertices not including v, which is
> (n - 1)(n - 2) / 2.". So if you want to get values between 0 and 1, divide
> the betweenness centrality values by (n-1)(n-2)/2.
>
> --
> Tamas
>
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