Cepheus is the first poker playing program that “essentially weakly solved” the game of heads-up limit Texas hold ’em. This was the first imperfect information game played competitively by humans to be essentially solved. It was developed by the Computer Poker Research Group (CPRG) at the University of Alberta and was introduced in January 2015 in a paper entitled “Heads-up limit hold’em poker is solved”, published in Science by Michael Bowling, Neil Burch, Michael Johanson, and Oskari Tammelin.
Researchers at the University of Alberta call this futuristic gambler Cepheus after a king from Greek mythology, and it is to poker what Deep Blue was to the game of chess. Also if you had designs on becoming the best poker player in the world, the computer’s designers have news for you: you’re destined for second place. The program was trained by playing billions of hands against itself, learning through trial-and-error the optimal strategy for one-on-one play. And while Cepheus’s programmers stop short of calling its strategy a perfect one, they say that it would never lose money against a human player over the long run.
What makes Cepheus special?
After all, computers have figured out how to solve games like checkers in the past. Well, say the scientists, games like checkers and Connect Four are different in that both players are privy to all of the information. Poker is unique in that a player must make their moves with a limited knowledge of what has happened up to that point. Assuming that every hand does not go to showdown, players must wonder when, why, and to what extent their opponents are bluffing. That aspect of the game is what draws players back to the felt, and it’s what makes this computer’s achievements so extraordinary.
What can you learn from Cepheus?
Humans may be outmatched by Cepheus, but the program may prove useful to new players of the game. By looking at the decisions the computer makes – most of them the correct ones for any given situation – players can see if their own games need refinement. Already, the computer proves that the player in the dealer position has a tremendous advantage in a heads up situation. It also proves that raising is preferable to calling in most situations, since it offers a way to immediately win the hand.
What’s most remarkable about the computer’s strategy is that it isn’t afraid to play loose. Cepheus will wade into competition with any number of dreadful hands, confident that it can use strategy to push the other player off a better set of cards. In this way, it is similar to many of the world’s top poker professionals like Ivey and Gus Hanson.
Cepheus’ strategy is very close to a Nash equilibrium strategy for heads-up limit Texas hold’em, as an optimal counter-strategy to Cepheus can only win 0.000986 big blinds per game on expectation (to go from “essentially” solving the game to just “solving” the game one has to reduce this expected loss to precisely 0 big blinds per game). However, 0.000986 big blinds per game on expectation means that even if someone played against Cepheus for a lifetime, this person will not be able to say, with statistical significance, that s/he has won.
Though Cepheus is garnering headlines for its poker-playing abilities, the researchers insist that training a computer to become a master gambler is little more than a side effect. They look at the imperfect-information game of poker as a symbol for more pressing real-world situations. One of the creators says that Cepheus’s strategy could be applied to fight terrorism, improve negotiations, and even treat disease.
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