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Ask HN: The ranking algorithm in 'the social network'

37 points by sdave ↗ HN
What was the ranking algorithm that is mentioned in the beginning of the movie? Eduardo writes some mathematical expression on the window (I am sure they were made up!). Actually what ranking strategies could be used in this scenario? I believe a ‘rank’ would have to include multiple parameters. Perhaps something in the lines of svms ?

11 comments

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adammcnamara
It's called the Elo Rating System (http://en.wikipedia.org/wiki/Elo_rating_system).

From the article, it's used to rank the relative skill of two players. It was created for chess, but I believe underpins most competitive ranking today including Xbox LIVE.

kersny
This is correct, and the equations in the movie were very much real. I thought it was funnily obvious when he called it "The algorithm for rating chess players", knowing what ELO was.

Here's "The Algorithm": http://imgur.com/e5myT

EDIT: In the intrest in contribution to discussion, two other methods for ranking are the Colley matrix from the BCS (http://www.colleyrankings.com/method.html) and I have used PageRank for a similar purpose before (http://michaelnielsen.org/blog/lectures-on-the-google-techno...).

carbocation
Nitpick: it's "Elo" because it's a man's last name, not an acronym.

Also, the Colley matrix homepage has this odd bit of text:

Please note: This method is copyright.

That's not how you protect algorithms.

endtime
Blizzard uses it for WoW and Starcraft II as well.
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piramida
Also I found interesting that the geek students considered this trivial formula a revelation. Does fall out of the context of the brilliant hacker culture :) When we needed a ranking system several years ago, I came up with this in half an hour, then figured out it already exists, is called Elo, and used everywhere, so we just copied their coefficients.
geebee
I had that reaction too... though I suspect that in "real life", geek students didn't consider this a revelation, just a good approach. Anyone who writes anything down in mathy notation in a hollywood movie is a "genius", worthy of mysterious background music.