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

[Gábor Csárdi]

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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