Search+Instability

a search phenomenon in alpha-beta and enhancements, where re-searches, most often with different windows leave contradicting results, for instance with aspiration windows at the root, an unexpected fail-low after a fail-high or vice versa. Beside other things, it may caused by graph history interaction or path-dependency in conjunction with the transposition table, as well as alpha-beta window dependencies of pruning decisions, like null move pruning, futility pruning, and history heuristic to decide about LMR. || [|Rayleigh–Taylor instability] in the [|Crab Nebula] ||~  ||^   || toc =Pragmatism= Some programmers abandon aspiration windows, while others don't immediately return from a PV-nodes in case of sufficient exact hits from transposition table.
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 * [[image:300px-Crab_Nebula.jpg link="http://en.wikipedia.org/wiki/File:Crab_Nebula.jpg"]] ||~  || **Search Instability**,

=Quotes= In his //Programming Topics//, Bruce Moreland elaborates on Search Instability :

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=See also=
 * Alpha-Beta
 * Aspiration Windows
 * Astronomy
 * Graph History Interaction
 * Path-Dependency
 * Principal Variation Search
 * Transposition Table
 * Window

=Forum Posts=

1994 ...

 * [|Alpha-beta inconsistencies] by Chua Kong Sian, rec.games.chess, February 19, 1994
 * [|Search inconsistency] by Bruce Moreland, rgcc, December 17, 1998
 * [|Question: Fail High then Low at Root] by William Bryant, CCC, December 28, 1999 » Fail-High, Fail-Low, Root

2000 ...

 * [|Fail highs..which subsequently fail low] by Tom King, CCC, August 27, 2000 » Fail-High, Fail-Low
 * [|Search Inconsistencies] by mjlef, Winboard Forum, June 23, 2006

2010 ...

 * [|Fail-High / Fail-Low in mate situations...] by Steve Maughan, CCC, August 24, 2013
 * [|Fail low after fail high] by J. Wesley Cleveland, CCC, April 04, 2015 » Fail-Low, Fail-High
 * [|Ordering of Root moves and search instability !] by Mahmoud Uthman, CCC, October 26, 2015 » Move Ordering
 * [|Shifting alpha/beta on hash hit] by Martin Fierz, CCC, April 14, 2016 » Transposition Table

=External Links=
 * [|Search Instability] from Bruce Moreland's [|Programming Topics]
 * [|Aspiration Windows] from Bruce Moreland's [|Programming Topics]
 * [|Instability from Wikipedia]

=References= =What links here?= include page="Search Instability" component="backlinks" limit="60"
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