It was close, but Houdini was the best computer chess program in the end.
In a competition called Thoresen Computer Engines Competition, which ended Thursday, Houdini, a free program, finished just ahead of Rybka, which has won the last four computer world chess championships.
The competition was a double round-robin (meaning each computer played all the others twice, once with each color), and it used the Bilbao Scoring System in which each win counts as 3 points and each draw as 1. Houdini finished with 24 points and Rybka with 23.
Stockfish, another free program, finished third, with 20 points, while Ivanhoe and Critter, yet another free program, tied for fourth and fifth, with 17 points each, though Ivanhoe was fourth on a tie-breaker.
Early in the tournament, it looked as if Houdini would run away from the field as it won its four games. But it slowed down after that, drawing eight of its last nine games.
Meanwhile, Rybka, which started by losing two of its first four games, came roaring back by winning five of its last nine games. If not for a loss to Shredder in Round 13, Rybka might have overtaken Houdini and won the tournament.
It was an interesting competition because there were clearly differences in style between the computer engines â€” a reflection of how they were designed and programmed.
Over all, 24 of the 56 games ended decisively. Though the programs are obviously not perfect, they are better at playing chess than humans. That so many of the games were decisive would suggest that there is still a great deal that is not known about chess. (If more was known, presumably strategies could be programmed into the computers so that they would not lose.) It seems that we are still a long way from â€œsolvingâ€ chess, as opposed to checkers, for example, which was solved several years ago.