Francesco Elia created SPARK-20429:
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             Summary: [GRAPHX] Strange results for personalized pagerank if 
node is involved in a cycle
                 Key: SPARK-20429
                 URL: https://issues.apache.org/jira/browse/SPARK-20429
             Project: Spark
          Issue Type: Bug
          Components: GraphX
    Affects Versions: 2.1.0
            Reporter: Francesco Elia


I'm trying to run the personalized PageRank implementation of GraphX on a 
simple test graph, which is the following: 

Image: https://i.stack.imgur.com/JDv1l.jpg

I'm a bit confused on some results that I get when I try to compute the PPR for 
a node that is involved in a cycle. For example, the final output for the node 
12 is as follows:

(13, 0.0141)
(7,  0.0141)
(19, 0.0153)
(17, 0.0153)
(20, 0.0153)
(11, 0.0391)
(14, 0.0460)
(15, 0.0541)
(16, 0.0541)
(12, 0.1832)

I would clearly expect that the node 13 would have a much higher PPR value (in 
fact, I would expect it to be the first one after the starting node itself). 
The problem appears as well with other nodes involved in cycles, for example 
for starting node 13 the node 15 has a very low score. From all the testing 
that I have done it seems that for starting nodes that do not participate in a 
cycle the result is exactly how I expect.



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