[HAMA-406] Pagerank wrong ALPHA

• Type: Bug
• Status: Resolved
• Priority: Blocker
• Resolution: Fixed
• Fix Version/s: 0.3.0
• Assignee: Edward J. Yoon
• Reporter: Thomas Jungblut
• Created: 24/Jun/11 09:11
• Updated: 24/Jun/11 09:24
• Resolved: 24/Jun/11 09:24

Description

Email:

---------- Forwarded message ----------
From: Yunkai Zhang <[e-mail]>
Date: Fri, Jun 24, 2011 at 9:51 AM
Subject: A bug in the PageRank example
To: [e-mail]

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 = 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).