Re: [igraph] Directed Leading Eigenvector

[Tamas Nepusz]

> Is there a specific reason why the directed version of leading
> eigenvector hasn't been included?
I think there isn't... as I recall, Gabor ported the symmetric  
eigensolver first from ARPACK and it wasn't suitable for directed  
graphs. Now we have an interface to ARPACK's symmetric and  
nonsymmetric solvers as well (see igraph_arpack_rssolve() and  
igraph_arpack_rnsolve() in src/arpack.c), so the directed version  
could be done as well -- we just simply didn't have the time for it. I  
think it's just a matter of using igraph_arpack_rnsolve, using two  
degree vectors instead of one (one for the out-degrees and another one  
for the in-degrees) and adapting the vector-matrix multiplication  
routine that's used internally by  
igraph_i_community_leading_eigenvector in src/community.c.

> I'd be happy to help write it if need be.
Well, if you are willing to work on it, let me know, I can give you a  
few pointers to start with and I'll be happy to help should you get  
stuck. Otherwise I will add the directed version to our ever growing  
wishlist and try to implement it for the next major release, but I  
can't tell you when that's gonna happen.

--
Tamas