Fruit is a

chess engine In computer chess, a chess engine is a computer program that analyzes chess or chess variant positions, and generates a move or list of moves that it regards as strongest. A chess engine is usually a back end with a command-line interface wit ...

developed by Fabien Letouzey. In the SSDF rating list released on November 24, 2006, Fruit version 2.2.1 had a rating of 2842. In the CEGT rating list released on January 24, 2007, Fruit version 2.2.1 had a rating of 2776.

History

At the

World Computer Chess Championship World Computer Chess Championship (WCCC) is an event held periodically since 1974 where computer chess engines compete against each other. The event is organized by the International Computer Games Association. It is often held in conjunction with ...

Reykjavík Reykjavík ( ; ) is the capital and largest city of Iceland. It is located in southwestern Iceland, on the southern shore of Faxaflói bay. Its latitude is 64°08' N, making it the world's northernmost capital of a sovereign state. With a po ...

in 2005, Fruit 2.2 scored 8.5 out of 11, finishing in second place behind Zappa. Until Version 2.1 (''Peach''), Fruit was free and open-source software subject to the requirements of the

GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general ...

and as such contributed much to the development in computer chess in recent years. Some people still work on the v2.1

source code In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the w ...

and have created variations from the original Fruit. As of July 23, 2007, Fruit became

freeware Freeware is software, most often proprietary, that is distributed at no monetary cost to the end user. There is no agreed-upon set of rights, license, or EULA that defines ''freeware'' unambiguously; every publisher defines its own rules for t ...

. Fruit 2.3.1 was one of the top 3 free UCI chess engines.

Technical details of Fruit 2.1

Fruit uses the classical

Negascout Principal variation search (sometimes equated with the practically identical NegaScout) is a negamax algorithm that can be faster than alpha-beta pruning. Like alpha-beta pruning, NegaScout is a directional search algorithm for computing the minima ...

(

principal variation A variation can refer to a specific sequence of successive moves in a turn-based game, often used to specify a hypothetical future state of a game that is being played. Although the term is most commonly used in the context of Chess analysis, it has ...

search) algorithm with iterative deepening to traverse the game tree. It also uses the

null-move heuristic In computer chess programs, the null-move heuristic is a heuristic technique used to enhance the speed of the alpha-beta pruning algorithm. Rationale Alpha-beta pruning speeds the minimax algorithm by identifying ''cutoffs'', points in the game ...

. The original version used a simplistic

evaluation function An evaluation function, also known as a heuristic evaluation function or static evaluation function, is a function used by game-playing computer programs to estimate the value or goodness of a position (usually at a leaf or terminal node) in a g ...

with a robust search. Later versions have improved evaluation functions. The board representation is distinct — Fruit uses a 16x16 board.

Derivatives

Although in 2007 Fabien Letouzey stopped the development of Fruit with version 2.3.1, the earlier open source 2.1 version provided the basis for many other programs.

Toga II

Toga II is a derivative created by Thomas Gaksch, currently continued by Jerry Donald Watson. It has more chess knowledge, multi-processor support, and perhaps a better search algorithm.Fruit Chess Engine by Fabien Letouzey
/ref> It is based on Fruit 2.1 and is free. The strongest version is '
Toga II 4.0
'', released on 29 December 2017 by Jerry Donald Watson. Experimental versions of Toga II running on

computer cluster A computer cluster is a set of computers that work together so that they can be viewed as a single system. Unlike grid computers, computer clusters have each node set to perform the same task, controlled and scheduled by software. The comp ...

s have competed in the World Computer Chess Championship (WCCC). At about 80 ELO above Fruit 2.3.1, Toga II is the strongest Fruit derivative . In 2008, forks of Toga II started to appear, like Grapefruit and Cyclone.

GambitFruit

GambitFruit is another free derivative of Fruit 2.1, created by Ryan Benitez. It plays a more aggressive style and has more chess knowledge. GambitFruit also incorporates improvements from Toga II. Development of GambitFruit stopped in 2005.

GNU Chess

GNU Chess GNU Chess is a free software chess engine and command-line interface chessboard. The goal of GNU Chess is to serve as a basis for research, and as such it has been used in numerous contexts. GNU Chess is free software, licensed under the terms ...

6.x is based on Fruit 2.1 and the project is since 2011 under active development.

Fruit Reloaded

Fruit Reloaded by Fabien Letouzey, Daniel Mehrmann and Ryan Benitez is an independent fork of Fruit 2.1 with a number of enhancements.

Rybka controversy

In June 2011, a lengthy investigation by the International Computer Games Association (ICGA) determined Rybka was plagiarized from Fruit and

Crafty Crafty is a chess program written by UAB professor Dr. Robert Hyatt, with continual development and assistance from Michael Byrne, Tracy Riegle, and Peter Skinner. It is directly derived from Cray Blitz, winner of the 1983 and 1986 World Compu ...

. The author of

Rybka Rybka is a computer chess engine designed by International Master Vasik Rajlich. Around 2011, Rybka was one of the top-rated engines on chess engine rating lists and won many computer chess tournaments. After Rybka won four consecutive World ...

, Vasik Rajlich, refused to address the allegations against Rybka with the ICGA, instead preferring an ''ex post facto'' public interview conducted by Nelson Hernandez on July 4, 2011. Rajlich had previously said: ''I went through the Fruit 2.1 source code forwards and backwards and took many things.''

Senpai

On the tenth anniversary of the start of Fruit development in 2014, Fabien Letouzey released a completely new engine, Senpai, under the GPLv3. Senpai makes use of chess engine developments made in the intervening decade. It differs from Fruit in using bitboards and C++11's thread support for SMP.

References

{{reflist, 30em

External links

Official Fruit HomepageFruit 2.1 source
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Fruit derivatives

Toga II Developers Discussion BoardGrapefruitFruit ReloadedCCRL website
2004 software Chess engines