Querg

[[toc]]
**[[Home]] * [[Engines]] * Querg**

**Querg**,
a series of [[Private Engines|private chess programs]] written by [[John F. White]] in [[6502]] [[Assembly|assembly]] to run on an 64K [[Atari 8-bit|Atari 130XE]], as described in the [[ICGA Journal#11_23|ICCA Journal, Vol. 11, Nos. 2/3]], 1988 <ref>[[John F. White]] (**1988**). //Querg Chess//. [[ICGA Journal#11_23|ICCA Journal, Vol. 11, Nos. 2/3]]</ref>. The name Querg has no meaning, the Querg P Quigel fictional character <ref>[[http://pathfinderfl.wordpress.com/2011/02/26/i-querg-p-quigel/|I, Querg P Quigel « Pathfinder's Federation Log]]</ref> from [[http://en.wikipedia.org/wiki/Star_Trek:_Voyager|Star Trek Voyager]] [[http://en.wikipedia.org/wiki/Pathfinder_%28Star_Trek:_Voyager%29|Pathfinder]] appeared some years later. Versions mentioned in the article were dubbed //NovaQuerg// and //SuperQuerg//. In his second [[ICGA Journal#13_1|ICCA Journal]] article, White describes how to store and retrieve moves of an [[Opening Book|opening book]] <ref>[[John F. White]] (**1990**). //The Amateur's Book-Opening Routine//. [[ICGA Journal#13_1|ICCA Journal, Vol. 13, No. 1]]</ref>.

=Description=
==Move Generation==
Most versions of Querg used a [[Mailbox|mailbox]] based offset [[Move Generation|move generation]], [[0x88]] techniques coupled with offset move generation are mentioned in the article, and that this technique has advantages for in [[Check#Detection|check detection]] as applied in [[Paul Wiereyn|Paul Wiereyn's]] mate finding program <ref>[[Paul Wiereyn]] (**1985**). //Inventive Problem Solving//. [[ICGA Journal#8_4|ICCA Journal, Vol. 8, No. 4]]</ref>. The experiments with [[Incremental Updates|incremental updated]] [[Move List|movelists]] were not that successful.

==Check Detection==
[[Check|Checks]] were first [[Check#Detection|detected]] by a variant of the method given by Wiereyn, modified to suit a cylindrical representation of the chess board, and rather slower than the original described - the 12 x 10 board is not well suited to implementation of this procedure. The alternative method to delay check detection until a king has been captured saved time in positions where checks are rare, but was inefficient if kings are vulnerable to checks. Finally, White came up with a technique to determine whether pieces give check during generation time.

==Search==
Querg applies [[Principal Variation Search|PVS]] with [[Aspiration Windows|Aspiration windows]] within an [[Iterative Deepening|iterative deepening]] framework, where the [[Principal variation|Principal variation]] is 'fed over' into the next iteration. Two [[Killer Move|killer moves]] were stored and used to [[Killer Heuristic|reject moves]]. Lazy move generation of [[PV-Move|PV-]] and killer moves before constructing a whole move list failed to provide any benefit. Forcing moves, that is [[Check|checks]] and replies to check, [[Promotions|promotions]], threats of promotions by the side not to move, and [[Captures|captures]], are [[Extensions|extended]] by a maximum of three additional plies in the whole path. A special routine //HIPL// (high-ply-[[Pruning|pruning]]) avoids the unnecessary sequence [[Make Move|make move]] -> [[Evaluation|evaluate]] -> [[Unmake Move|unmake move]] at [[Frontier Nodes|frontier nodes]] for none forcing moves.

==Evaluation==
The [[Evaluation|evaluation]] relies largely on first-order terms <ref>[[Jan Eric Larsson]] (**1987**). //Challenging that Mobility is Fundamental//. [[ICGA Journal#10_3|ICCA Journal, Vol. 10, No. 3]]</ref>, considering [[Material|material]], pieces left [[En prise|en prise]], [[Mobility|mobility]] as number of moves plus information from [[Piece-Square Tables|piece-square tables]], and [[Pawn Structure|pawn structure]].

=Performance=
Performance was determined by [[Test-Positions|test-positions]] and games played versus programs running on the same 8-bit Atari, such as [[Cyrus]], [[Colossus Chess|Colossus 3.0]], the old [[Sargon|Sargon 2.5]], and others, where //NovaQuerg// finished with 6.5 points out of 14. However, Querg has not played any official tournaments.

=See also=
* [[Various Classifications#Startrek|Star Trek]]
* [[Quark]]

=Publications=
<ref>[[http://ilk.uvt.nl/icga/journal/docs/References.pdf|ICGA Reference Database]] (pdf)</ref> 
* [[John F. White]] (**1988**). //Querg Chess//. [[ICGA Journal#11_23|ICCA Journal, Vol. 11, Nos. 2/3]]
* [[John F. White]] (**1990**). //The Amateur's Book-Opening Routine//. [[ICGA Journal#13_1|ICCA Journal, Vol. 13, No. 1]]

=External Links=
* [[http://www.mobygames.com/game/querg-draughts|Querg Draughts for Atari ST (1994) - MobyGames]]
* [[http://pathfinderfl.wordpress.com/category/star-trek-online/page/3/|Star Trek Online « Pathfinder's Federation Log]]
* [[http://pathfinderfl.wordpress.com/2011/02/26/i-querg-p-quigel/|I, Querg P Quigel « Pathfinder's Federation Log]]
* [[http://pathfinderfl.wordpress.com/stotoons/querg/|Lt Cmd Querg « Pathfinder's Federation Log]]

=References= 
<references />
=What links here?= 
[[include page="Querg" component="backlinks" limit="40" ]]
**[[Engines|Up one level]]**