Re: [igraph] page.rank speed

[Tamás Nepusz]

> page.rank has been running forever:
[...]
> on
> 
> IGRAPH DN-- 12062801 15279166 --
> attr: name (v/c)
> 
> is this normal?
Not sure but I wouldn't rule it out -- your graph is pretty large and ARPACK 
can be a tad bit slow. I have just tried it on an Erdos-Renyi graph of similar 
size and it also did not terminate for a while. On the other hand, you might be 
experiencing a convergence issue with ARPACK. Sometimes it happens that ARPACK 
fails to detect convergence (at least within the machine epsilon) and performs 
the maximum number of allowed iterations with essentially no improvement after 
the first few iterations -- then it bails out with a warning saying that the 
maximum number of iterations has been reached. Try increasing the epsilon value 
a bit when invoking page.rank() to see if it terminates faster or not. Or 
decrease the maximum number of iterations allowed. I'm not familiar with the R 
interface but I think there is an options=... argument to page.rank where you 
can specify some options that ARPACK will use.

An alternative solution if you are feeling adventurous and you don't mind 
compiling igraph from source: try the 0.7-prpack branch of igraph (downloadable 
from Github):

https://github.com/igraph/igraph/tree/0.7-prpack

This branch uses the excellent PRPACK package instead of ARPACK to calculate 
PageRank scores. PRPACK does all sorts of neat tricks to ensure faster 
convergence for PageRank calculations. The branch will be merged with the 0.7 
development tree sooner or later but it still needs more testing.

All the best,
Tamas