Author: Robert Hyatt
Date: 12:29:39 01/22/98
Go up one level in this thread
On January 22, 1998 at 13:50:10, Stuart Cracraft wrote: >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! the 2*iteration number won't be enough by itself for sure. You can find this limit in early versions of crafty sources when I was doing the threat extension. It helped, but not enough. however I didn't limit it to near the tips either, because it was also useful nearer to the root where it is just as profitable to extend when there is a threat. But it is also expensive...
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