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

[Tamas Nepusz]

Hi Vincent,

It could be the case that the Windows and Linux versions use different
bit length for the variables that store the betweenness values, so the
values that cause overflow on Windows do not cause overflow on Linux.
Just a guess, but the issue that you have submitted is still a valid
one, so it will be fixed eventually.

All the best,
T.

T.


On Mon, Sep 14, 2015 at 10:18 AM, Vincent Labatut
<address@hidden> wrote:
> Done: https://github.com/igraph/igraph/issues/865
>
> Note that I've tried again on Linux (the first try was on Windows), and for
> some reason it seems to work (with the same igraph version).
>
> Cheers,
>
> Vincent
>
>> Ah, my bad, I did not notice that you meant the edge betweenness and
>> not the node betweenness. It looks like the edge betweenness related
>> code does not include a similar bigint workaround. This should be
>> fixed in the next version then - can you add a bug report to
>> https://github.com/igraph/igraph/issues ?
>>
>> Thanks,
>> T.
>>
>>> On Sun, Sep 13, 2015 at 9:24 AM, Vincent Labatut <address@hidden> wrote:
>>> Hello Tamas,
>>>
>>> and thanks for your answer.
>>> I was thinking of something like that, since the networks are lattices
>>> and
>>> this case is mentionned in the documentation.
>>> I also had noticed the "nobigint" parameter for the "betweenness"
>>> functions,
>>> however it does not exist for the "edge.betweenness" functions.
>>> Best,
>>> Vincent
>>>
>>>> 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.
>>>>
>>>>
>>>>
>>>> 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
>>>>>
>
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