Editing Chess engine (section)

==Increasing strength==
Chess engines increase in playing strength continually. This is partly due to the increase in processing power that enables calculations to be made to ever greater depths in a given time. In addition, programming techniques have improved, enabling the engines to be more selective in the lines that they analyze and to acquire a better positional understanding. A chess engine often uses a vast previously-computed opening "book" to increase its playing strength for the first several moves, up to possibly 20 moves or more in deeply analyzed lines.{{citation needed|date=June 2017}}
[[File:Chess ability of the best computers.png|right|upright=1.5|frameless]]
Some chess engines maintain a database of chess positions, along with previously-computed evaluations and best moves—in effect, a kind of "dictionary" of recurring chess positions.  Since these positions are pre-computed, the engine merely plays one of the indicated moves in the database, thereby saving computing time, resulting in stronger, faster play.

Some chess engines use [[endgame tablebase]]s to increase their playing strength during the [[chess endgame|endgame]]. An endgame tablebase includes all possible endgame positions with a small amount of material. Each position is conclusively determined as a win, loss, or draw for the player whose turn it is to move, and the number of moves to the end with best play by both sides. The tablebase identifies for every position the move which will win the fastest against an optimal defense, or the move that will lose the slowest against an optimal offense. Such tablebases are available for all chess endgames with seven pieces or fewer (trivial endgame positions are excluded, such as six white pieces versus a lone black [[king (chess)|king]]).<ref>[http://tb7.chessok.com/shared-positions http://tb7.chessok.com] {{Webarchive|url=https://web.archive.org/web/20201201214914/http://tb7.chessok.com/shared-positions |date=2020-12-01 }} Lomonosov website allowing registered user to access 7-piece tablebase, and a forum with positions found.</ref><ref>[https://www.chess.com/forum/view/endgames/who-wins-from-this-puzzle "Who wins from this? (chess puzzle)"] {{Webarchive|url=https://web.archive.org/web/20201111220720/https://www.chess.com/forum/view/endgames/who-wins-from-this-puzzle |date=2020-11-11 }} An example chess position found from the Lomonosov chess tablebase.</ref>

When the maneuvering in an ending to achieve an irreversible improvement takes more moves than the horizon of calculation of a chess engine, an engine is not guaranteed to find the best move without the use of an endgame tablebase, and in many cases can fall foul of the [[fifty-move rule]] as a result. Many engines use [[permanent brain]] (continuing to calculate during the opponent's turn) as a method to increase their strength.

[[Distributed computing]] is also used to improve the software code of chess engines. In 2013, the developers of the [[Stockfish (chess)|Stockfish]] chess playing program started using distributed computing to make improvements in the software code.<ref>{{cite web|url=http://tests.stockfishchess.org/tests|title=Stockfish Testing Framework|website=Tests.stockfishchess.org|access-date=7 March 2014|archive-date=22 March 2014|archive-url=https://web.archive.org/web/20140322122039/http://tests.stockfishchess.org/tests|url-status=live}}</ref><ref>{{cite web|url=http://stockfishchess.org/get-involved/|title=Get Involved|website=Stockfishchess.org|access-date=8 March 2014|archive-date=16 June 2013|archive-url=https://web.archive.org/web/20130616211650/http://stockfishchess.org/get-involved/|url-status=live}}</ref><ref>{{cite web | url=http://www.talkchess.com/forum/viewtopic.php?start=0&t=47885&topic_view=flat&sid=b5662f579ad4c7bea91668bb9d9723a4 | title=Fishtest Distributed Testing Framework | date=1 May 2013 | last=Costalba | first=Marco | website=Talkchess.com | access-date=18 April 2014 | archive-date=19 April 2014 | archive-url=https://web.archive.org/web/20140419012854/http://www.talkchess.com/forum/viewtopic.php?start=0&t=47885&topic_view=flat&sid=b5662f579ad4c7bea91668bb9d9723a4 | url-status=live }}</ref> {{As of|2017|6}}, a total of more than 745 years of CPU time has been used to play more than 485 million chess games, with the results being used to make small and incremental improvements to the chess-playing software.<ref>{{cite web | url=http://tests.stockfishchess.org/users | title=Stockfish Testing Framework - Users | website=Test.stockfishchess.org | access-date=17 June 2017 | archive-date=25 June 2018 | archive-url=https://web.archive.org/web/20180625233351/http://tests.stockfishchess.org/users | url-status=dead }}</ref> In 2019, Ethereal author Andrew Grant started the distributed computing testing framework OpenBench, based upon Stockfish's testing framework,<ref>{{cite web|url=https://github.com/andygrant/openbench|title=Github - AndyGrant/OpenBench: OpenBench is a Distributed SPRT Testing Framework for Chess Engines|website=Github.com|access-date=23 December 2021|archive-date=23 December 2021|archive-url=https://web.archive.org/web/20211223142116/https://github.com/andygrant/openbench|url-status=live}}</ref><ref>{{Cite web|title=OpenBench|url=http://chess.grantnet.us/|access-date=2022-02-16|website=Chess.grantnet.us|archive-date=2022-02-16|archive-url=https://web.archive.org/web/20220216060628/http://chess.grantnet.us/|url-status=live}}</ref> and it is now the most widely-used testing framework for chess engines.{{Citation needed|date=February 2022}}