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

[Yong Zou]

Hi Tamas,

I tried to use "%f" but the results are the same with very big
negative values, like -31394965001799.761719 or 28275655826861.414062.
There must be something wrong, which I have to figure out. I have no
idea to deal with.

>> Furthermore, I have got some floating numbers for the betweenness.
>> This is also interesting for me because BC of a vertex "is the number
>> of geodesics going through it". This means BC should be integer
>> values, doesn't it?
>
> Not necessarily; suppose that there are two shortest paths from vertex A to
> vertex B - they are equal and minimal in length but they are not exactly the
> same. In this case, both paths count only with a weight of 0.5. In general,
> if there are k different shortest paths between two given vertices, they all
> count with a weight of 1/k

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. I'm quite confused by this now. The values should be
normalized to the interval [0 1]?

How does it calculate in igraph for the BC?

Thanks,
Yong