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Hydra is a chess machine, designed by a team with Dr. Christian "Chrilly" Donninger, GM Christopher Lutz. Hydra is under the patronage of the PAL Group and Sheikh Tahnoon Bin Zayed Al Nahyan of Abu Dhabi. The goal of the Hydra Project is to dominate the computer chess world, and finally have an accepted victory over humans.

Hydra represents a potentially significant leap in the strength of computer chess. Lorenz estimates its FIDE equivalent playing strength to be over ELO 3000, and this is in line with its results against Michael Adams and Shredder 8, the former micro-computer chess champion.

The Hydra team originally planned to have Hydra appear in four versions: Orthus, Chimera, Scylla and then the final Hydra version — the strongest of them all. The original version of Hydra evolved from an earlier design called Brutus and works in a similar fashion to Deep Blue, utilising large numbers of purpose-designed chips (in this case implemented as a field-programmable gate array or FPGA). In Hydra, there are multiple computers, each with its own FPGA acting as a chess coprocessor. These coprocessors enable Hydra to search enormous numbers of positions per second, making each processor more than ten times faster than an unaided computer.

Hydra currently runs on a 64 node Xeon cluster, with a total of 64 gigabytes of RAM. It evaluates about 200,000,000 chess positions per second, roughly the same as the much older Deep Blue, but with several times more overall computing power. Whilst FPGAs generally have a lower performance level than ASIC chips, modern-day FPGAs run about as fast as the older ASICs used for Deep Blue. The engine is on average able to evaluate up to a depth of about 18 ply (9 moves by each player), deeper than Deep Blue, which only evaluated to about 12 ply on average. Hydra's search uses alpha-beta pruning as well as null-move heuristics [1]. The extra search depth over Deep Blue is due to its use of more modern type B forward pruning techniques that can miss some possibilities but generally play better due to the greater search depth permitted^{[citation needed]}.

The Hydra computer is physically located in Abu Dhabi, in the United Arab Emirates, and is usually operated over a network link.

• In July 2002, Brutus finished 3rd in the World Computer Chess Championship in Maastricht, the Netherlands. It drew two games and lost one, giving it a score of 7.0 out of 9. The loss, against Deep Junior, included a rook sacrifice for very long term compensation, which the additional computing power of Brutus could not help it to understand.

• In November 2003, Brutus finished 4th in the World Computer Chess Championship in Graz, Austria. It lost two games and drew one, giving it a score of 8.5 out of 11. This disappointing result left the team to find a new sponsor, which they found in the form of the PAL group.

• In April 2004, Hydra finished second in the International CSVN Tournament in Leiden, the Netherlands. It lost one game and drew 3, leaving it with 6.5 points out of 9, 1.5 points behind winner Shredder. A loss out of the opening led to the hiring of GM Christopher Lutz, who made a new opening book.

• In August 2004, at the 14th Abu Dhabi International Chess Festival, Hydra played an eight game match against the computer program Shredder 8, a multiple-times world computer chess champion. Running on "just" 16 nodes Hydra defeated Shredder 5.5 - 2.5, winning three games and drawing the rest. In an informal match at the same tournament, Hydra took on International Grandmaster Evgeny Vladimirov of Kazakhstan, and defeated him by a score of 3.5 - 0.5.

• In October 2004, in a man vs. machine contest, Hydra defeated former FIDE world champion Ruslan Ponomariov in both of their games. Ponomariov had an ELO rating of 2710 at the time of the match.

• In February 2005, Hydra won the 14th IPCCC (International Paderborn Computer Chess Championships) tournament. Hydra scored 8 out of 9 (seven wins and two draws), defeating chess program Shredder again in the process.

• Due to human handler errors and program errors, Hydra did not fare well in the June 2005 PAL/CSS Freestyle Chess Tournament, an online tournament where players are allowed to access any and all resources to them, including computer engines, databases, as well as human grandmasters. Two versions of Hydra participated in the tournament- Hydra Chimera (without human intervention) scored 3.5/8, and Hydra Scylla (with human intervention) scored 4/8. Neither version of Hydra qualified for the quarter-finals.

• From June 21 to June 27, 2005, Hydra played a six game match against Michael Adams, the top British player and ranked 7th in the world. The prize fund was $145,000, paid out on a per game basis: a win netting $25,000, a draw $10,000 to both players, and a loss nothing. Hydra defeated Adams by a score of 5.5 - 0.5; Adams lost each game except for game 2 which he drew. This version of Hydra was running on half power; only 32 out of 64 nodes were utilized. Adams played against the Scylla version of Hydra.

Hydra plays 28. Bxh6!!, leading Adams to resign

• In November 2005, Hydra played 4 games: it beat Rustam Kasimdzhanov, drew with Alexander Khalifman, beat Ruslan Ponomariov and finally drew with Rustam Kasimdzhanov.

• In the April 2006 PAL/CSS Freestyle Chess Tournament Hydra finished first with a score of 5.5/7, a full point ahead of the field. This tournament allows for any human or computer aid including teams. All 64 of Hydra's nodes were utilized.

• In the June 2006 PAL/CSS Freestyle Chess Main Tournament Hydra finished tied for 5th-16th.

Hydra has so far no loss on record against an unaided human player in over-the-board play. Hydra has, however, been beaten by humans who had access to the advice of other programs during their games; for example, correspondence chess International Grandmaster Arno Nickel beat an older version of Hydra in a two-game correspondence match lasting six months. The 32 node version that played against Adams managed to draw Nickel in their third game, which lasted five months and ended in December 2005.

• Computer Chess

• Hydrachess
• Hydra's games on ChessGames.com
• game 3 against Arno Nickel (07/11/2005)
• Play through the games of the Adams vs Hydra 2005 Match
• Beginning of New Yorker article on Hydra, Your Move: Chrilly Donninger's Hydra, computer chess program by Tom Muelle, The New Yorker, December 12, 2005