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

[Szabolcs Horvát]

Just to have a simple test case:

Based on a comparison with Mathematica, for an n*n grid graph things
start to go wrong at n=35. For n=34 the edge betweenness is still
accurate.

On 13 September 2015 at 22:37, Tamas Nepusz <address@hidden> wrote:
> 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.
>
> 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
>>>>
>>
>>
>> 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
>>
>>
>>
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>>
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