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From SWP <contact-sem...@unister-gmbh.de>
Subject Multiple aggregators & PageRank example
Date Tue, 22 May 2012 08:54:33 GMT

looking at the example PageRank.java (revision 1341332), it appears that:
- within PageRankVertex.compute, we have numEdges=1 for a vertex without
outgoing edges, because each is assigned a self-loop in line 114,
pageJob.set("hama.graph.self.ref", "true");
- the corresponding "random surfer" will leave a vertex without outgoing
edges (apart from the self-loop) with a probability of
(1-DAMPING_FACTOR) = 0.15, assuming the default settings are used

I would like to change this behaviour such that:
- vertices never have loops
- the random surfer leaves a vertex without outgoing edges with
probability 1

However this implies that I will have to sum up globally the probability
mass over all vertices without outgoing edges and redistribute it
uniformly over the graph.  This should happen in addition to the 0.15
restart probability.

Now, aggregators seem to be the concept in Hama to support this kind of
global communication.
But there can only be one aggregator, and it is already in use to
facilitate the stopping criterion.

Is there a way to support more than one aggregator?  Should I write a
new aggregator class that somehow supports both tasks?  And am I getting
things right anyway? ;-)

Clemens Gröpl


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