Internal+Iterative+Deepening

used in nodes of the search tree in a iterative deepening depth-first alpha-beta framework, where a program has no best move available from a previous search PV or from the transposition table. **IID** is used to find a good move to search first by searching the current position to a reduced depth, and using the best move of that search as the first move at the real depth. IID was already introduced by John J. Scott in 1969 inside his program Lancaster, and further elaborated by Thomas Anantharaman in 1991 , as used in Deep Thought with a reduction of 2 plies at PV-nodes and cut-nodes with no best-move information from the transposition table. While it is pretty much a washout on average, Deep Though used this heuristic since it makes the search times more predictable by avoiding those isolated instances when the search time suddenly becomes 10 times larger than expected. || Internal/External Form ||~ ||^ || toc =Reduction= The main implementation detail of IID comes with how to reduce the search. Typical reductions include -1, -2, /2, or /4. Some also use either the minimum or the maximum of a subtraction and a division.
 * Home * Search * Move Ordering * Internal Iterative Deepening**
 * [[image:180px-Henry_Moore_at_Kew_Gardens_563.JPG link="https://commons.wikimedia.org/wiki/File:Henry_Moore_at_Kew_Gardens_563.JPG"]] ||~ || **Internal Iterative Deepening (IID)**,
 * Henry Moore: Large Upright

=Conditions= Where to use IID is also an important question. Limiting the depth is an obvious condition (only use IID if depth > 5, say). Most only use IID in PV-Nodes, but it is also possible to use it at predicted Cut-Nodes.

=Insurance= Harm Geert Muller in a reply to Stan Arts on the insurance aspect of IID, in a CCC discussion why IID does not work some programs like Movei and RomiChess

=Publications=
 * John J. Scott (**1969**). //A chess-playing program//. [|Machine Intelligence 4]
 * Thomas Anantharaman (**1991**). //Extension Heuristics//. 1.12 Internal iterative deepening, ICCA Journal, Vol. 14, No. 2

=See also=
 * Double Null Move
 * Iterative Deepening
 * Multi–ProbCut
 * Node Types

=Forum Posts=

1998 ...

 * [|Internal Iterative Deepening] by Roberto Waldteufel, CCC, August 12, 1998

2000 ...

 * [|Crafty internal iterative deepening] by Tijs van Dam, CCC, January 26, 2000 » Crafty
 * [|MTD, IID, fail-low, root-research] by Juergen Wolf, CCC, August 14, 2003 » MTD(f), Fail-Low, Root

2005 ...

 * [|Something obious on IID that not everybody does] by Dann Corbit, Winboard Forum, March 04, 2006
 * [|self deepening: an improved implementation of IID] by Harm Geert Muller, Winboard Forum, April 24, 2006
 * [|Re: movei hash report] by Harm Geert Muller, CCC, August 13, 2007 » Movei
 * [|Internal Iterative Deepening] by Andrew Short, CCC, September 24, 2008
 * [|Null driven IID] by Marco Costalba, CCC, December 08, 2008

2010 ...

 * [|iid and singular extensions] by Daniel Shawul, CCC, July 05, 2010 » Singular Extensions
 * [|Trouble with IID] by kenny stanley, CCC, February 20, 2011
 * [|On internal iterative deepening] by Onno Garms, CCC, March 13, 2011 » Onno, Node Types
 * [|Internal Iterative Deepening questions] by Alcides Schulz, CCC, September 21, 2011
 * [|Reductions from internal iterative deepening] by Evert Glebbeek, CCC, August 20, 2012 » Reductions
 * [|IID and move sorting] by Daniel Shawul, CCC, May 09, 2013 » ABDADA
 * [|What do you use IID for] by Daniel Shawul, CCC, December 10, 2013
 * [|IFD vs IID] by Sergei S. Markoff, CCC, January 30, 2014
 * [|Fail soft vs fail hard] by Sergei S. Markoff, CCC, February 15, 2014 » Fail-Soft, Fail-Hard, Fail-Low

2015 ...

 * [|Hash Refutation] by Dennis Sceviour, CCC, August 24, 2015 » Schooner
 * [|Mate scores from IID] by Matthew R. Brades, CCC, August 16, 2016 » Mate Score
 * [|Value of IID] by Thomas Kolarik, CCC, August 25, 2016
 * [|improving iid] by Folkert van Heusden, CCC, January 06, 2017
 * [|(I)ID and PV dropout] by Harm Geert Muller, CCC, June 17, 2017 » Aspiration Windows, Fail-Low, Iterative Deepening
 * [|IID (skipped when in check and Score greater than alpha)] by Tamás Kuzmics, CCC, July 24, 2017

=External Links=
 * [|µ-Max Search: Iterative Deepening] by Harm Geert Muller

=References= =What links here?= include page="Internal Iterative Deepening" component="backlinks" limit="200"
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