[jira] [Commented] (SPARK-20839) Incorrect Dynamic PageRank calculation

["Andrew Ray (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-20839?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16049214#comment-16049214 ] 

Andrew Ray commented on SPARK-20839:
------------------------------------

1 & 2 work together to do the algorithm properly with an active set, this is by design.
3 although it may look wrong, the deltas (and thus messages) will always be positive so this is not a problem.

> Incorrect Dynamic PageRank calculation
> --------------------------------------
>
>                 Key: SPARK-20839
>                 URL: https://issues.apache.org/jira/browse/SPARK-20839
>             Project: Spark
>          Issue Type: Bug
>          Components: GraphX
>    Affects Versions: 2.1.1
>            Reporter: BahaaEddin AlAila
>
> Correct me if I am wrong
> I think there are three places where the pagerank calculation is incorrect
> 1st) in the VertexProgram (line 318 of PageRank.scala in spark 2.1.1)
> val newPR = oldPR + (1.0 - resetProb) * msgSum
> it should be
> val newPR = resetProb + (1.0 - resetProb) * msgSum
> 2nd) in the message sending part (line 336 of the same file)
> Iterator((edge.dstId, edge.srcAttr._2 * edge.attr))
> should be 
> Iterator((edge.dstId, edge.srcAttr._1 * edge.attr))
> as we should be sending the edge weight multiplied by the current pagerank of the source vertex (not the vertex's delta)
> 3rd) the tol check against the abs of the delta (line 335)
>       if (edge.srcAttr._2 > tol) {
> should be
>       if (Math.abs(edge.srcAttr._2) > tol) {
>  



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