Fail-Soft

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 =History= In his 1983 paper //Another optimization of alpha-beta search//, John Philip Fishburn introduced Fail-Soft Alpha-Beta as an improvement of Fail-Hard without any extra work. Fail-Soft has the reputation for searching less nodes than Fail-Hard, but might also require some care regarding to search instability issues in conjunction with transposition tables and various pruning-, reduction- and extension techniques.
 * Fail-Soft** is a term related to an Alpha-Beta like search. Returned scores might be outside the bounds:
 * an upper bound less than alpha at All-Nodes
 * a lower bound greater than beta at Cut-Nodes

=Mate Scores= In Chrilly Donninger's initial null move pruning implementation there was a deep search extension, if the null move was refuted by a mate attack, thus relying on Fail-Soft of a null window search, where many "random" moves may refute the null-move with or without score in the mate range.

=See also=
 * Fail-Hard
 * Fail-High
 * Fail-Low
 * Principal Variation Search
 * NegaScout
 * NegaC*
 * MTD(f)

=Publications=
 * John Philip Fishburn (**1983**). //[|Another optimization of alpha-beta search]//. SIGART Bulletin, Issue 84, [|pdf]

=Forum Posts=

1995 ...

 * [|New improvement to alpha/beta + TT?] by Heiner Marxen, rgcc, January 13, 1997
 * [|Fail-soft with PVS?] by Will Singleton, CCC, March 09, 1999 » Principal Variation Search
 * [|What is the advantage of fail-soft?] by Bas Hamstra, CCC, August 25, 1999

2000 ...

 * [|Fail-soft or Fail-hard ?] by Teerapong Tovirat, CCC, November 04, 2000 » Fail-Hard
 * [|Alpha beta fail soft, pruning & hash bounds?] by Steve Maughan, CCC, December 14, 2000 » Pruning, Bound
 * [|Fail Soft Alpha Beta & Transpositions] by Orhan Öztürk, rgcc, September 3, 2003
 * [|(Fail soft) alpha beta] by Delphi, rgcc, September 4, 2003
 * [|Fail soft alpha-beta] by Russell Reagan, CCC, September 08, 2003
 * [|Is this a correct fail-soft?] by Mikael Bäckman, CCC, September 21, 2003
 * [|My fail soft reduces quality of collected PV. Help needed] by Volker Böhm, CCC, April 20, 2004
 * [|Fail-hard, fail-soft question] by Dan Honeycutt, CCC, May 06, 2004

2005 ...

 * [|Fail Soft question] by David B. Weller, CCC, February 17, 2006
 * [|Search questions] by Sven Schüle, Winboard Forum, July 17, 2007 » Mate Distance Pruning, Principal Variation Search
 * [|mate detetion issue] by Mike Adams, CCC, October 24, 2008 » Checkmate, Connect Four
 * [|fail soft vs fail hard] by cyberfish, CCC, November 19, 2008
 * [|Return eval or upper bound?] by John Merlino, CCC, October 26, 2009

2010 ...

 * [|First post (and FailHigh question!)] by Natale Galioto, CCC, June 14, 2013 » Fail-High, Fail-Hard
 * [|Fail soft vs fail hard] by Sergei S. Markoff, CCC, February 15, 2014 » Fail-Hard, Fail-Low, Internal Iterative Deepening
 * [|Implications of Lazy eval on Don Beal effect in Fail Soft] by Henk van den Belt, CCC, November 19, 2014 » Lazy Evaluation

2015 ...

 * [|Multi-cut and fail-soft] by Matthew R. Brades, CCC, June 30, 2016 » Multi-Cut

=External Links= > Lineup: [|Mike Ratledge], John Marshall, Karl Jenkins, [|Roy Babbington], Allan Holdsworth > media type="youtube" key="6zSZBAcQ-5M" width="560" > Lineup: [|Ray Russell], Ian Carr, [|Brian Smith], Karl Jenkins, John Marshall, [|Roy Babbington] > media type="youtube" key="nnDgalLCFfw"
 * [|Fail soft from Wikipedia]
 * Soft Machine - [|Hazard Profile] (1975), [|YouTube] Video
 * Ian Carr's [|Nucleus] - Song For The Bearded Lady (1970), [|YouTube] Video

=References= =What links here?= include page="Fail-Soft" component="backlinks" limit="80"
 * Up one Level**