Re: [igraph] edge.betweenness returns negative or NaN values

[Tamas Nepusz]

Hello,

The negative values are most likely due to integer overflows (i.e. the
betweenness score would be too large and the underlying variable in
which igraph computes the betweenness score overflows). You can get
around this by passing nobigint=FALSE to the edge betweenness call -
it will make igraph use "big integers", which can hold arbitrarily
large numbers at the expense of being somewhat slower.

As for the NaNs, it could be a bug, but let's see first whether the
issue persists with nobigint=FALSE. If so, let us know and try to post
a small example on which we could reproduce the issue with NaNs.

T.


T.


On Sat, Sep 12, 2015 at 3:08 PM, Vincent Labatut
<address@hidden> wrote:
> Hello,
>
> I am processing the edge-betweenness of various networks using R igraph
> version 7.1. Those are spatial networks (each node has a (x,y) position) and
> I am using the "weight" option of the "edge.betweenness" function to take
> the spatial distances into account. This spatial distance is stored in an
> edge attribute called "dist".
>
> Here is the command I use:
> edge.betweenness(graph=g, weights=E(g)$dist)
>
> However, for some of my networks, I get negative values, or even NaN. Here
> are two examples, under the graphml format:
> http://dx.doi.org/10.6084/m9.figshare.1540708
> - scale=32.graphml
> - scale=41.graphml
>
> For the first one, the first values returned by "edge.betweenness" are:
>    [1] 1904887544.08 1904887544.08 1896303182.39 1951787568.72 1203043060.76
>    [6] 1270869072.68  622780616.09  667964773.27  279064394.68  309184936.21
>   [11]  135403467.81  155266075.94   51600202.02   60120695.31   21113003.39
>   [16]   24783603.89    6275147.30    6937885.52    1347425.01    1002544.99
>   [21]     150574.42    -327097.77    -711849.38   -1430744.36    -246214.20
>   [26]    -602827.15    -230344.97    -484630.12    -297768.08    -492364.06
>
> For the second one, all the returned values are NaN.
>
> Note that all these weights are positive by definition. They even are
> non-zero since no two nodes hold the same position, by construction. I also
> checked this programmatically. Moreover, there are no multiple links, also
> by construction (and I checked with "has.multiple").
>
> I was wondering if the negative or NaN values I get are due to me misusing
> the function, or if this is a bug in igraph.
>
> Thanks,
> Vincent Labatut
>
> _______________________________________________
> igraph-help mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/igraph-help
>