Editing Computer chess (section)

== Computers versus humans ==
{{Main|Human–computer chess matches}}

After discovering refutation screening—the application of [[alpha–beta pruning]] to optimizing move evaluation—in 1957, a team at [[Carnegie Mellon University]] predicted that a computer would defeat the world human champion by 1967.<ref>{{cite journal|last1=Simon|first1=H.A.|last2=Newell|first2=A.|title=Heuristic problem solving: The next advance in operations research|journal=Operations Research|date=1958|volume=6|issue=1|page=7|doi=10.1287/opre.6.1.1|url=https://home.mis.u-picardie.fr/~furst/docs/Newell_Simon_Heuristic_Problem_Solving_1958.pdf|access-date=10 February 2018}}</ref> It did not anticipate the difficulty of determining the right order to evaluate moves. Researchers worked to improve programs' ability to identify [[killer heuristic]]s, unusually high-scoring moves to reexamine when evaluating other branches, but into the 1970s most top chess players believed that computers would not soon be able to play at a [[Senior Master (chess)|Master]] level.{{r|hapgood19821223_30}} In 1968, [[International Master]] [[Computer chess bet|David Levy made a famous bet]] that no chess computer would be able to beat him within ten years,{{r|douglas197812}} and in 1976 [[Senior Master (chess)|Senior Master]] and professor of psychology [[Eliot Hearst]] of [[Indiana University]] wrote that "the only way a current computer program could ever win a single game against a master player would be for the master, perhaps in a drunken stupor while playing 50 games simultaneously, to commit some once-in-a-year blunder".{{r|hapgood19821223_30}}

In the late 1970s chess programs began defeating highly skilled human players.{{r|hapgood19821223_30}} The year of Hearst's statement, [[Northwestern University]]'s [[Chess 4.5]] at the [[Paul Masson]] American Chess Championship's [[Chess title#Expert|Class B]] level became the first to win a human tournament. Levy won his bet in 1978 by beating [[Chess 4.7]], but it achieved the first computer victory against a Master-class player at the tournament level by winning one of the six games.<ref name="douglas197812">{{cite news | url=https://archive.org/stream/byte-magazine-1978-12/1978_12_BYTE_03-12_Life#page/n85/mode/2up | title=Chess 4.7 versus David Levy | work=BYTE | date=December 1978 | access-date=17 October 2013 | author=Douglas, J R | page=84}}</ref> In 1980, [[Belle (chess machine)|Belle]] began often defeating Masters. By 1982 two programs played at Master level and three were slightly weaker.{{r|hapgood19821223_30}}

The sudden improvement without a theoretical breakthrough was unexpected, as many did not expect that Belle's ability to examine 100,000 positions a second—about eight plies—would be sufficient. The Spracklens, creators of the successful microcomputer program ''[[Sargon (chess)|Sargon]]'', estimated that 90% of the improvement came from faster evaluation speed and only 10% from improved evaluations. ''[[New Scientist]]'' stated in 1982 that computers "play ''terrible'' chess ... clumsy, inefficient, diffuse, and just plain ugly", but humans lost to them by making "horrible blunders, astonishing lapses, incomprehensible oversights, gross miscalculations, and the like" much more often than they realized; "in short, computers win primarily through their ability to find and exploit miscalculations in human initiatives".<ref name="hapgood19821223_30"/>

By 1982, microcomputer chess programs could evaluate up to 1,500 moves a second and were as strong as mainframe chess programs of five years earlier, able to defeat a majority of amateur players. While only able to look ahead one or two plies more than at their debut in the mid-1970s, doing so improved their play more than experts expected; seemingly minor improvements "appear to have allowed the crossing of a psychological threshold, after which a rich harvest of human error becomes accessible", ''New Scientist'' wrote.{{r|hapgood19821223_30}} While reviewing ''SPOC'' in 1984, ''[[BYTE]]'' wrote that "Computers—mainframes, minis, and micros—tend to play ugly, inelegant chess", but noted [[Robert Byrne (chess player)|Robert Byrne]]'s statement that "tactically they are freer from error than the average human player". The magazine described ''SPOC'' as a "state-of-the-art chess program" for the IBM PC with a "surprisingly high" level of play, and estimated its USCF rating as 1700 (Class B).<ref name="byte198403">{{cite news | url=https://archive.org/stream/byte-magazine-1984-03-rescan/1984_03_BYTE_09-03_Simulation#page/n289/mode/2up | title=SPOC / The Chess Master | work=BYTE | date=March 1984 | access-date=8 September 2015 |author1=Flock, Emil |author2=Silverman, Jonathan | pages=288–294}}</ref>

At the 1982 [[North American Computer Chess Championship]], [[Monroe Newborn]] predicted that a chess program could become world champion within five years; tournament director and International Master [[Michael Valvo]] predicted ten years; the Spracklens predicted 15; [[Ken Thompson]] predicted more than 20; and others predicted that it would never happen. The most widely held opinion, however, stated that it would occur around the year 2000.<ref name="stinson198201">{{cite news | url=http://www.cgwmuseum.org/galleries/index.php?year=1982&pub=6&id=3 | title=Chess Championship: Machines Play, People Watch | work=Softline | date=Jan 1982 | access-date=13 July 2014 | author=Stinson, Craig | page=6}}</ref> In 1989, Levy was defeated by [[Deep Thought (chess computer)|Deep Thought]] in an exhibition match. Deep Thought, however, was still considerably below World Championship level, as the reigning world champion, [[Garry Kasparov]], demonstrated in two strong wins in 1989. It was not until a 1996 match with [[International Business Machines|IBM's]] [[IBM Deep Blue|Deep Blue]] that Kasparov lost his first game to a computer at tournament time controls in [[Deep Blue versus Kasparov, 1996, Game 1|Deep Blue versus Kasparov, 1996, game 1]]. This game was, in fact, the first time a reigning world champion had lost to a computer using regular time controls. However, Kasparov regrouped to win three and [[draw (chess)|draw]] two of the remaining five games of the match, for a convincing victory.

In May 1997, an updated version of Deep Blue defeated Kasparov 3½–2½ in a return match. A documentary mainly about the confrontation was made in 2003, titled ''[[Game Over: Kasparov and the Machine]]''.

{{Chess diagram
|tright
|[[Deep Blue versus Kasparov, 1996, Game 1|Deep Blue vs. Kasparov, 1996, game 1]]

|  |  |  |  |  |  |  |
|  |  |  |  |  |  |  |rl
|  |  |  |  |  |qd|  |kd
|  |  |  |ql|  |  |nl|
|  |  |  |pd|  |  |  |
|pl|pl|  |  |  |pd|pl|pl
|  |  |  |  |  |nd|  |kl
|  |  |  |  |rd|  |  |
|Final position
}}

With increasing processing power and improved evaluation functions, chess programs running on commercially available workstations began to rival top-flight players. In 1998, [[REBEL (chess)|Rebel 10]] defeated [[Viswanathan Anand]], who at the time was ranked second in the world, by a score of 5–3. However, most of those games were not played at normal time controls. Out of the eight games, four were [[blitz chess|blitz]] games (five minutes plus five seconds [[Time control#Chess|Fischer delay]] for each move); these Rebel won 3–1. Two were semi-blitz games (fifteen minutes for each side) that Rebel won as well (1½–½). Finally, two games were played as regular tournament games (forty moves in two hours, one hour sudden death); here it was Anand who won ½–1½.<ref>{{cite web|url=http://www.rebel.nl/anand.htm |title=Rebel vs Anand |publisher=Rebel.nl |access-date=2010-04-03}}</ref> In fast games, computers played better than humans, but at classical time controls – at which a player's rating is determined – the advantage was not so clear.

In the early 2000s, commercially available programs such as [[Junior (chess program)|Junior]] and [[Fritz (chess)|Fritz]] were able to draw matches against former world champion Garry Kasparov and classical world champion [[Vladimir Kramnik]].

In October 2002, Vladimir Kramnik and Deep Fritz competed in the eight-game [[Brains in Bahrain]] match, which ended in a draw. Kramnik won games 2 and 3 by "conventional" [[anti-computer tactics]] – play conservatively for a long-term advantage the computer is not able to see in its [[game tree]] search. Fritz, however, won game 5 after a severe blunder by Kramnik. Game 6 was described by the tournament commentators as "spectacular".  Kramnik, in a better position in the early [[Chess middlegame|middlegame]], tried a piece sacrifice to achieve a strong tactical attack, a strategy known to be highly risky against computers who are at their strongest defending against such attacks. True to form, Fritz found a watertight defense and Kramnik's attack petered out leaving him in a bad position. Kramnik resigned the game, believing the position lost. However, post-game human and computer analysis has shown that the Fritz program was unlikely to have been able to force a win and Kramnik effectively sacrificed a drawn position. The final two games were draws.  Given the circumstances, most commentators still rate Kramnik the stronger player in the match.{{Citation needed|date=January 2008}}

In January 2003, Kasparov played [[Junior (chess program)|Junior]], another chess computer program, in New York City. The match ended 3–3.

In November 2003, Kasparov played [[X3D Fritz]].  The match ended 2–2.

In 2005, [[Hydra (chess)|Hydra]], a dedicated chess computer with custom hardware and sixty-four processors and also winner of the 14th [[International Paderborn Computer Chess Championship|IPCCC]] in 2005, defeated seventh-ranked [[Michael Adams (chess player)|Michael Adams]] 5½–½ in a six-game match (though Adams' preparation was far less thorough than Kramnik's for the 2002 series).<ref>{{cite web|url=http://www.chessbase.com/newsdetail.asp?newsid=2476 |title=Chess News – Adams vs Hydra: Man 0.5 – Machine 5.5 |date=28 June 2005 |publisher=ChessBase.com |access-date=2010-04-03}}</ref>

In November–December 2006, World Champion Vladimir Kramnik played Deep Fritz.  This time the computer won; the match ended 2–4. Kramnik was able to view the computer's opening book. In the first five games Kramnik steered the game into a typical "anti-computer" positional contest. He lost one game ([[Blunder of the century|overlooking a mate in one]]), and drew the next four. In the final game, in an attempt to draw the match, Kramnik played the more aggressive [[Sicilian Defence]] and was crushed.

There was speculation that interest in human–computer chess competition would plummet as a result of the 2006 Kramnik-Deep Fritz match.<ref>[https://www.nytimes.com/2006/12/05/crosswords/chess/05cnd-chess.html Once Again, Machine Beats Human Champion at Chess] New York Times, December 5, 2006</ref> According to Newborn, for example, "the science is done".<ref>{{cite news| url=https://www.nytimes.com/2006/12/05/crosswords/chess/05cnd-chess.html | work=The New York Times | title=Once Again, Machine Beats Human Champion at Chess | date=5 December 2006 | access-date=30 April 2010}}</ref>

Human–computer chess matches showed the best computer systems overtaking human chess champions in the late 1990s. For the 40 years prior to that, the trend had been that the best machines gained about 40 points per year in the [[Elo rating]] while the best humans only gained roughly 2 points per year.<ref>[http://www.ddj.com/hpc-high-performance-computing/184405171 Computer Chess: The Drosophila of AI] October 30, 2002</ref> The highest rating obtained by a computer in human competition was Deep Thought's USCF rating of 2551 in 1988 and FIDE no longer accepts human–computer results in their rating lists. Specialized machine-only Elo pools have been created for rating machines, but such numbers, while similar in appearance, are not directly compared.<ref>[http://www.aaai.org/ojs/index.php/aimagazine/article/viewFile/753/671 Deep Thought wins Fredkin Intermediate Prize], [[Hans Berliner]]</ref> In 2016, the [[Swedish Chess Computer Association]] rated computer program [[Komodo (chess)|Komodo]] at 3361.

[[Chess engine]]s continue to improve. In 2009, chess engines running on slower hardware reached the [[Grandmaster (chess)|grandmaster]] level. A [[mobile phone]] won a [[category (chess tournament)|category]] 6 tournament with a performance rating 2898: chess engine [[Hiarcs]] 13 running inside [[Pocket Fritz]] 4 on the mobile phone [[HTC Touch HD]] won the Copa Mercosur tournament in [[Buenos Aires]], Argentina with 9 wins and 1 draw on August 4–14, 2009.<ref name=PF4GM>{{cite web|url=https://theweekinchess.com/html/twic771.html#13 |title=Pocket Fritz 4 wins Copa Mercosur |publisher=Chess.co.uk |access-date=2010-04-03 |url-status=dead |archive-url=https://web.archive.org/web/20110930232108/https://theweekinchess.com/html/twic771.html#13 |archive-date=2011-09-30 }}</ref> Pocket Fritz 4 searches fewer than 20,000 positions per second.<ref name=PF420K>Stanislav Tsukrov, Pocket Fritz author. [http://hiarcs.net/forums/viewtopic.php?t=2537&start=67 Pocket Fritz 4 searches less than 20,000 positions per second.]</ref> This is in contrast to supercomputers such as Deep Blue that searched 200&nbsp;million positions per second.

[[Advanced Chess]] is a form of chess developed in 1998 by Kasparov where a human plays against another human, and both have access to computers to enhance their strength. The resulting "advanced" player was argued by Kasparov to be stronger than a human or computer alone. This has been proven in numerous occasions, such as at Freestyle Chess events.

Players today are inclined to treat chess engines as analysis tools rather than opponents.<ref>{{cite web|url=http://www.dw.com/en/world-chess-champion-magnus-carlsen-the-computer-never-has-been-an-opponent/a-19186058|title=World chess champion Magnus Carlsen: 'The computer never has been an opponent'|publisher=Deutsche Welle|date=16 April 2016|access-date=26 August 2016}}</ref> Chess grandmaster [[Andrew Soltis]] stated in 2016 "The computers are just much too good" and that world champion [[Magnus Carlsen]] won't play computer chess because "he just loses all the time and there's nothing more depressing than losing without even being in the game."<ref name="npr 20 years">{{cite news |title=20 Years Later, Humans Still No Match For Computers On The Chessboard |url=https://www.npr.org/sections/alltechconsidered/2016/10/24/499162905/20-years-later-humans-still-no-match-for-computers-on-the-chessboard |access-date=28 June 2020 |work=NPR.org |date=2016 |language=en}}</ref>