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'''[[Main Page|Home]] * [[Search]] * [[Alpha-Beta]] * Aspiration Windows'''
[[FILE:TheNon-EuclideanWindow.JPG|border|right|thumb|The Non-Euclidean Window <ref>[[Arts#GerhardHoehme:Category:Gerhard Hoehme|Gerhard Hoehme]] - The Non-Euclidean Window (1964), mixed technique / wood on canvas, [[Arts#ArtMuseumBochum:Category:Art Museum Bochum|Art Museum]], [https://en.wikipedia.org/wiki/Bochum Bochum], [https://en.wikipedia.org/wiki/North_Rhine-Westphalia North Rhine-Westphalia], [https://en.wikipedia.org/wiki/Germany Germany], part of [[:Category:Industrial Heritag Trail|The Industrial Heritage Trail]] of the [https://en.wikipedia.org/wiki/Ruhr Ruhr area], Photo by [[Gerd Isenberg]], October 30, 2016</ref> ]]
'''Aspiration windows''' are a way to reduce the [[Search Space|search space]] in an alpha-beta search. The technique is to use a guess of the expected value (usually from the last iteration in [[Iterative Deepening|iterative deepening]]), and use a [[Window|window]] around this as the alpha-beta [[Bound|bounds]]. Because the window is narrower, more beta cutoffs are achieved, and the search takes a shorter time. The drawback is that if the true score is outside this window, then a costly re-search must be made. Typical window sizes are 1/2 to 1/4 of a pawn on either side of the guess.
instead. However, a fully fledged search is typically full of [[Search Instability|search instability]], and it will often happen that the above re-search will fail low! This is why it is best to only widen the bound that fails, and leave the other bound unchanged.
Modern engines, like [[RobbolitoRobboLito]] or [[Stockfish]], start with a rather small aspiration window, and increase the bound that fails in an exponential fashion.
=PVS and Aspiration=
* [http://www.talkchess.com/forum/viewtopic.php?t=46837 Aspiration Windows] by [[Jerry Donald]], [[CCC]], January 11, 2013
* [http://www.talkchess.com/forum/viewtopic.php?t=47996 Aspiration windows] by [[Marco Pampaloni]], [[CCC]], May 14, 2013
* [http://www.talkchess.com/forum/viewtopic.php?t=53972 Your experience with PVS + Aspiration window] by [[Fabio Gobbato]], [[CCC]], October 07, 2014 » [[Principal Variation Search]], [[PVS and aspirationAspiration]]
* [http://www.talkchess.com/forum/viewtopic.php?t=54241 Solving a fail low situation at the root] by [[Alberto Sanjuan]], [[CCC]], November 03, 2014 » [[Fail-Low]]
==2015 ...==
* [http://www.talkchess.com/forum/viewtopic.php?t=57113 Parallel aspiration windows] by [[Giuseppe Cannella]], [[CCC]], July 29, 2015
* [http://www.talkchess.com/forum/viewtopic.php?t=58542 Restarting iterative deepening] by [[Harm Geert Muller]], [[CCC]], December 09, 2015 » [[Fail-Low]], [[Iterative Deepening]]
* [http://www.talkchess.com/forum/viewtopic.php?t=60285 Dynamic aspiration window] by [[Sergei Markoff|Sergei S. Markoff]], [[CCC]], May 26, 2016
* [http://www.talkchess.com/forum/viewtopic.php?t=60402 Aspiration Windows on the root search -- Determining margin] by [[Andrew Grant]], [[CCC]], June 08, 2016
* [http://www.talkchess.com/forum/viewtopic.php?t=60916 Iterative Deepening Question] by [[David Cimbalista]], [[CCC]], July 23, 2016 » [[Iterative Deepening]]
* [http://www.open-chess.org/viewtopic.php?f=5&t=2995 Aspiration window with TT question] by [[Sander Maassen vd Brink|sandermvdb]], [[Computer Chess Forums|OpenChess Forum]], August 01, 2016 » [[Transposition Table]]
'''20162017 ...'''
* [http://www.talkchess.com/forum/viewtopic.php?t=63706 Conceptual question on aspiration windows] by Jacob Wilkins, [[CCC]], April 09, 2017
* [http://www.talkchess.com/forum/viewtopic.php?t=64321 (I)ID and PV dropout] by [[Harm Geert Muller]], [[CCC]], June 17, 2017 » [[Fail-Low]], [[Internal Iterative Deepening]], [[Iterative Deepening]]
* [http://www.talkchess.com/forum/viewtopic.php?t=65589 Aspiration window problem] by [[Sander Maassen vd Brink]], [[CCC]], October 30, 2017
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=68278&start=16 Re: Lazy SMP ideas] by [[Folkert van Heusden]], [[CCC]], October 03, 2018 » [[Lazy SMP]]
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=69627 Impact of Aspiration on tree size] by Frank Kopp, [[CCC]], January 16, 2019
=External Links=
'''[[Alpha-Beta|Up one level]]'''
[[Category:Gerhard Hoehme]][[Category:Art Museum Bochum]][[Category:Industrial Heritag Heritage Trail]]
