
Ask HN: The ranking algorithm in 'the social network' - sdave
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 ?
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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.

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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...](http://michaelnielsen.org/blog/lectures-on-the-google-
technology-stack-1-introduction-to-pagerank/)).

~~~
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.

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kersny
Ah, yes, my mistake. And I wonder how that copyright works... it seems as
though these guys:
[http://digital.ipcprintservices.com/publication/?i=34502&...](http://digital.ipcprintservices.com/publication/?i=34502&p=17)
used the method for their project, although I don't think they made any money
off of it. That article also describes Colley's matrix very 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.

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alphaoverlord
There was an interesting statistics/modelling competition on Kaggle for
different approaches to chess ranking.

<http://kaggle.com/chess>

