Re: [igraph] igraph-help Digest, Vol 79, Issue 12

[Tamás Nepusz]

> I am finding it challenging to count the number of triangles between two 
> nodes say u and v for all u,v in N using R

If you mean the number of triangles that contain both u and v, for every u and 
v in the network, then you can use the cocitation function (igraph_cocitation 
in C, cocitation() in R, Graph.cocitation() in Python. This is because the 
number of triangles that involve both u and v is equal to the number of common 
neighbors of u and v, which is exactly what cocitation() calculates for an 
undirected graph. Note that cocitation() gives you a full matrix, i.e. you’ll 
get an n x n matrix for n vertices, so you cannot use it directly if your graph 
is large. In this case, you’ll have to iterate over the (u,v) pairs of interest 
on your own, fetch the neighbors, and then calculate the intersection.

T.