Re: [igraph] pagerank implementation questions

[Tamas Nepusz]

> One more question on the converge speed, I tried:
As I see, you only modified the niter value and did not take into  
account that it is used only as an upper bound on the number of  
iterations. In most of the cases, the algorithm converges earlier  
("converges" = "the difference between the vectors in the last two  
iterations are less than eps"). In the examples found in  
igraph_pagerank.c, it converges in 34 and 39 iterations, respectively  
- this can easily be checked by printing the value of the variable  
niter inside igraph_pagerank's implementation after the main loop. At  
that point, niter holds the number of _unused_ iteration  
possibilities (since niter starts from the value supplied when  
invoking igraph_pagerank and is decremented by one during each  
iteration).

I also don't know which variant of the PageRank algorithm (the  
normalized or the unnormalized one) did the original authors use in  
their paper, but it might also happen that the normalized version  
converges faster than the unnormalized one - or they might have used  
a different eps value.

> and is there an API in igraph to set the initial value?
Not yet, it is initialized to a uniform distribution (all PageRanks  
equal).

--
Tamas Nepusz <address@hidden>             MTA RMKI, BME MIT