Poker-playing computer program Cepheus devises ultimate strategy

For some poker players, today may be the day they fold their hopes of becoming the best in the world. A team of researchers at the University of Alberta has created a virtually invincible poker-player computer program, dubbed Cepheus.

By playing billions of hands against itself, Cepheus has learned the best strategy for heads-up, limit hold'em - a spin-off of the popular card game Texas hold'em, but with two players (heads-up) and fixed bet sizes (limit).

As a result, this poker variant has been essentially solved by the program, meaning it plays an almost perfect game.

"Even if you played 60 million hands of poker for 70 years, 12 hours a day, and never made any mistakes, you still wouldn't be able to say with statistical confidence you were better than this program," said study author and computer scientist Michael Bowling, who has worked on the project since 2003.

A perfect solution would mean a program would never lose money against an opponent in the long run. Bowling and his colleagues can't say that about Cepheus, but they know the computer can stay ahead for at least as long as any human can live.

"We're not quite perfect, but we're so close that even after a lifetime of playing against it, you wouldn't know it wasn't perfect," Bowling said. The study was published online in the journal Science.

Perfect solutions have been found for games such as Connect Four, but unlike poker, these are characterised as perfect-information games. In other words, players know everything that has happened in the game before making their move.