Original post: The Algorithm for Facemash in The Social Network
After some Googling, it would appear that the Facemash algorithm corresponds to the Elo rating system. Thus, the equations involved are:
Ea = 1/(1 + 10^((Rb -Ra)/400))
Eb = 1/(1 + 10^((Ra -Rb)/400))
I’m surprised to see this algorithm treated with such reverence in the movie. While it is sophisticated and useful, and has been used in official chess rankings for decades, it has recently taken a beating at the hands of modern data miners. As of 10/8/2010, ninety teams have developed more predictive methods than Elo ratings for handicapping chess matches: see the Kaggle contest leaderboard.