Author: Stuart Cracraft
Date: 13:17:35 01/22/98
Go up one level in this thread
On January 22, 1998 at 15:29:39, Robert Hyatt wrote: >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... How did you get a score to use for this extension? The original article advocates using the evaluation function at the interior tree nodes! I think this is far more expensive than the extension. --Stuart
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