YOUR MOVE.(Chrilly Donninger's Hydra, computer chess program)

Chrilly Donninger prefers to watch from a distance when Hydra, his computer chess program, competes, because he is camera-shy, but also because he rarely understands what Hydra is doing, and the uncertainty makes him nervous. During Hydra's match against the world's seventh-ranked player, Michael Adams, in London last June, Donninger sat with three grand masters at the back of a darkened auditorium, watching a video projection of the competition on the wall behind Adams. Most of the time, Donninger, a forty-nine-year-old Austrian, had little to worry about; Hydra won the match five games to none, with one draw. But in the second game, which ended in the draw, the program made an error that briefly gave its human opponent an advantage.

The game was played at a spotlit table on a low podium. Adams sat in the classic chess player's pose--his elbows resting on the table, his chin cupped in his palms--reaching out now and then with his right hand to move a piece on a large wooden chessboard. Across from him was Hydra--a laptop linked by Internet connection to a thirty-two-processor Linux cluster in Abu Dhabi--and Hydra's human operator, who entered Adams's moves into the computer and recorded the program's replies on the board. On the laptop's screen was a virtual chessboard showing the current position in the game, as well as a pane of swiftly scrolling numbers representing a fraction of the thousands of lines of play that Hydra was analyzing, and a row of colored bars that grew or shrank with each move, according to the program's assessment of who was winning--green bars meant an advantage for white, red bars for black.

For much of the match, the bars showed Hydra comfortably in the lead. When Adams made a mistake, they spiked dramatically, but mostly they grew in small increments, recording the tiny advantages that the program was steadily accumulating. Many of these were so subtle that Donninger and the grand masters failed to grasp the logic of Hydra's moves until long after they had been made. But about twenty minutes into the second game, when Hydra advanced its central e-pawn to the fifth rank, there was a small commotion in the group. Yasser Seirawan, an American player formerly ranked in the top ten, who had coached Adams for the match, gave a thumbs-up sign. Christopher Lutz, a German grand master who is Hydra's main chess adviser, groaned. Only Donninger, who programs chess far better than he plays it, was baffled. He turned to Lutz in alarm.

"What was that? What did you see?"

"Now our pawn structure has become inflexible," Lutz replied. "Do we have anything in the program for flexibility?"

"What do you mean by 'flexibility'?"

Lutz frowned. He sensed that Hydra had hemmed itself in, giving Adams the upper hand. Bishop to b7 was the correct move, Lutz believed--the most natural way for Hydra to preserve its attacking chances and its room to maneuver. But explaining his nebulous insights to a lesser player like Donninger was a challenge.