Implementing PageRank using MapReduce

Question

I\'m trying to get my head around an issue with the theory of implementing the PageRank with MapReduce.

I have the following simple scenario with three nodes: A B C.

Answer 1

We iteratively evaluate PR. PR(x) = Sum(PR(a)*weight(a), a in in_links) by

map ((url,PR), out_links) //PR = random at start
for link in out_links
   emit(link, ((PR/size(out_links)), url))

reduce(url, List[(weight, url)):
   PR =0
   for v in weights
       PR = PR + v
   Set urls = all urls from list

   emit((url, PR), urls)

so the output equals input and we can do this until coverage.