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Posted to dev@hama.apache.org by "Thomas Jungblut (JIRA)" <ji...@apache.org> on 2011/06/24 11:24:47 UTC
[jira] [Commented] (HAMA-406) Pagerank wrong ALPHA
[ 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 <be...@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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