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From "Thomas Jungblut (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HAMA-406) Pagerank wrong ALPHA
Date Fri, 24 Jun 2011 09:24:47 GMT

    [ https://issues.apache.org/jira/browse/HAMA-406?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13054322#comment-13054322
] 

Thomas Jungblut commented on HAMA-406:
--------------------------------------

Okay was already commited by edward.
Thanks.

> Pagerank wrong ALPHA
> --------------------
>
>                 Key: HAMA-406
>                 URL: https://issues.apache.org/jira/browse/HAMA-406
>             Project: Hama
>          Issue Type: Bug
>            Reporter: Thomas Jungblut
>            Assignee: Thomas Jungblut
>            Priority: Blocker
>             Fix For: 0.3.0
>
>
> Email:
> ---------- Forwarded message ----------
> From: Yunkai Zhang <bennyzyk@gmail.com>
> Date: Fri, Jun 24, 2011 at 9:51 AM
> Subject: A bug in the PageRank example
> To: hama-user@incubator.apache.org
> Hi,
> I am playing with the pagerank example from trunk and found there is a bug
> in the code.
> If I assign any value other than 0.85 to the damping factor, the results
> won't sum to 1.
> For example: Set damping factor to *0.5*
> 11/06/23 17:28:05 INFO graph.PageRankBase: -------------------- RESULTS
> --------------------
> 11/06/23 17:28:06 INFO graph.PageRankBase: stackoverflow.com |
> 0.052213531500120945
> 11/06/23 17:28:06 INFO graph.PageRankBase: nasa.gov | 0.04235399497763073
> 11/06/23 17:28:06 INFO graph.PageRankBase: facebook.com |
> 0.030321424044325564
> 11/06/23 17:28:06 INFO graph.PageRankBase: yahoo.com | 0.05650175656380897
> 11/06/23 17:28:07 INFO graph.PageRankBase: youtube.com |
> 0.025716796492259456
> 11/06/23 17:28:07 INFO graph.PageRankBase: google.com | 0.07350857237752877
> 11/06/23 17:28:07 INFO graph.PageRankBase: twitter.com |
> 0.030321424044325564
> The sum is 0.3ish.
> Therefore, I read the code. I think a possible reason is that the value of *
> ALPHA* is hard-coded. (Formula: P(i) = ALPHA + 0.85 * sum, ALPHA = 0.15 /
> NumVertices() )
> In PageRank.java, line 167: ALPHA = *0.15* / (double) numOfVertices;
> I think 0.15 should be replaced by (1 - DAMPING_FACTOR).
> ---------------------
> We have to change the alpha to (1 - DAMPING_FACTOR).

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