Author: Stuart Cracraft
Date: 10:50:10 01/22/98
Go up one level in this thread
On January 22, 1998 at 05:03:38, Ernst A. Heinz wrote: >On January 21, 1998 at 21:56:27, Robert Hyatt wrote: > >>On January 21, 1998 at 18:52:44, Heiko Mikala wrote: >> >>> >>>On January 19, 1998 at 04:21:26, Ernst A. Heinz wrote: >>> >>>>On January 18, 1998 at 18:53:15, Bruce Moreland wrote: >>>>>On January 18, 1998 at 10:37:59, Robert Hyatt wrote: >>>>> >>>>>>(...) The idea was to shift the null-move window downward, and >>>>>>then notice whether the null-move search fails high or low. If it fails low, >>>>>>(...) you extend by 1 ply. > >No, Bob, the idea as mentioned in Donninger's paper is different. Here >is >the reference for all who do not know the article. > >Donninger, C. (1993). >Null move and deep search: Selective search heuristics for obtuse chess >programs. ICCA Journal, Vol. 16, No. 3, pp. 137--143. > >Donninger's idea is to extend the search one ply if a null move near the >horizon (e.g. at depths <= 3) does not fail high and the null move score >plus a constant margin (e.g. minor piece value) is <= alpha while the >static evaluation at the node is >= beta (i.e. fails high). In order to >get meaningful results for the null move score, you need to do it with a >full alpha-beta window instead of a zero window (this is a known error >in >Donninger's original article). > >Citing from my article about how "DarkThought" plays chess: > >In order to avoid possibly explosive growth of the search tree as caused >by excessive deep search extensions in the case of repeated mutual >mating threats, "DarkThought" restricts them to null moves at depth = 2 >in the >first "2 * iteration-number" plies on all paths. > >>>I tried Bruce's mate threat extension (everyone did, I guess...), and it >>>works fine. > >I just gave it a quick shot but then put it on my to-do list because the >quick implementation made our search trees *explode* ... :-( > >=Ernst= It made my search tree explode too. I will try putting in the Dark Thought limitations of depth = 2 and the first 2 * iteration-number plies. Thanks for the tip!
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