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Inside the 20-Year Quest to Build Computers That Play Poker

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Rivers Casino in Pittsburgh, PA.

Tuomas Sandholm and Noam Brown, the computer scientists at Carnegie Mellon who built Libratus, celebrated the win as the first time a computer has beaten top poker players at a variant of unlimited Texas holdem, the worlds most prominent poker game.

Credit: Ross Mantle/Bloomberg Businessweek

Four of the best professional poker players in the world spent most of January holed up at the Rivers Casino in Pittsburgh, losing. They’d show up before 11 AM, wearing sweatpants and stylish sneakers, and sit down in front of computer screens. Each of them was supposed to play 1,500 hands of heads-up no limit Texas Hold ‘Em online before they could go back to the hotel for the night. This often meant working past 10 p.m. Over the course of the day, Starbucks cups and water bottles piled up next to the players's keyboards. Chipotle bags lay at their feet. 

Every time one of the players made a move, the action was transmitted to a computer server sitting five miles away at Carnegie Mellon University. From there, a signal would travel another 12 miles to their opponent, a piece of software called Libratus running at the Pittsburgh Supercomputing Center in Monroeville, a nearby suburb. Libratus played eight hands at once — two against each opponent. It moved at a deliberate pace, slow enough to drive Jason Les, one of its human opponents, a bit mad. “It makes the days longer,” said Les, an earnest, athletic-looking man who seemed eager to take a few minutes off one afternoon last week. “Waiting should not affect me whatsoever, but sometimes you’re just like, 'OK, is this going to be over yet?'” 

Libratus, of course, never needs a break. It's different from human players in other ways, too. People tend to think longer when there’s more money at stake. The computer plays most slowly on small pots, a result of having to scroll through all the additional possibilities that come from having more chips remaining in its hand. Libratus also tends to make huge, sudden wagers, violating standard betting conventions by throwing its money into the pot in irregular amounts and at odd intervals.

Coming from a human player, behavior like this would be irritating, reckless and, over the long run, expensive. But Libratus’s main attribute as a poker player is that it’s inhumanly good. When the 20-day tournament at Rivers came to an end Monday, the humans had lost $1.8 million. (They didn’t actually have to pony up the cash; money serves as the way of keeping score in poker.) Tuomas Sandholm and Noam Brown, the computer scientists at Carnegie Mellon who built Libratus, celebrated the win as the first time that a computer has beaten top poker players at a variant of unlimited Texas hold’em, the world’s most prominent poker game. 

Experts in artificial intelligence have always used games as a way to develop and test their creations. Computers have surpassed the best human players at chess, checkers, backgammon, and go. Poker is a distinct challenge because of the element of chance, and because the players don’t know what cards their opponents are holding. So-called imperfect information games require the sort of human intelligence — like deceiving an opponent and sensing when she’s deceiving you— that computers lack.


From Bloomberg Technology
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