Almost every Friday at 3pm there is a talk at McGill’s Computer Science department. Today was definitely one of the coolest ones: two members of the team that won the Netflix prize gave a talk on their machine learning techniques. Martin Chabbert and Martin Piotte, graduates of the Ecole Polytechnique de Montreal were members of BellKor Pragmatic Chaos that won the $1 million, 20 minutes before the deadline. Among the most interesting lessons in their fascinating talk, was the fact that at the end they had intelligently combined about 800 predictors using machine learning techniques and clever approximations. However, as they said, it was becoming evident towards the end of the competition that the only way to win, by hitting the mark of 10% improvement on Netflix’s movie recommendation algorithm, was to join forces with other teams, namely BellKor and BigChaos — explains the weird team name. This meant sharing technical expertise, sharing predictors to be combined in ensemble classification, and of course sharing the money 🙂 Here are the technical documents that explain how they did it: Pragmatic Theory, BigChaos, BellKor.