Re: [igraph] Why are unconnected subgraphs not considered by motif counting functions?

[Szabolcs Horvát]

I didn't know about triad_census().  Thanks for the pointer!

On 16 July 2015 at 14:21, Gábor Csárdi <address@hidden> wrote:
> I cannot recall what the actual reason was, but one possible
> explanation is that even for moderately sized graphs, if they are
> sparse, you have a lot of those "motifs", more than what you can count
> in an 'int'.
>
> Btw. triad_census gives you the count for those "motifs" as well, and
> it already overflows for a ring with 10000 vertices and edges:
>
> triad_census(make_ring(10, directed = TRUE))
> #>  [1] 50 60  0  0  0 10  0  0  0  0  0  0  0  0  0  0
> triad_census(make_ring(10000, directed = TRUE))
> #>  [1] -271196661   99960000          0          0          0      10000
> #>  [7]          0          0          0          0          0          0
> #> [13]          0          0          0          0
>
> It does not even warn you, which is pretty bad, actually.....
>
> Gabor
>
> On Thu, Jul 16, 2015 at 3:21 AM, Szabolcs Horvát <address@hidden> wrote:
>> Dear All,
>>
>> igraph's motif counting functions (motifs()) will not count
>> unconnected subgraphs and always return NA for the 1st, 2nd and 4th
>> element of the result (for 3-motifs).
>>
>> The reasoning is that (quoting from the docs):
>>
>>>  Note that for unconnected subgraphs, which are not considered to be 
>>> motifs, the result will be NA.
>>
>> Is there any _technical_ reason for this behaviour?  I understand that
>> according to some definitions, unconnected subgraphs are not
>> considered motifs, but in many applications it is still useful to
>> count _all_ size-k subgraphs.
>>
>> It would be useful if motifs() returned all counts.  It is much easier
>> to simply ignore those I don't want (when I don't want them) than
>> having to separately count the missing ones.
>>
>> Szabolcs
>>
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