Author: Dieter Buerssner
Date: 10:01:57 04/20/04
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On April 20, 2004 at 12:52:47, Robert Hyatt wrote: >On April 20, 2004 at 11:50:29, Dieter Buerssner wrote: > >>On April 20, 2004 at 06:10:05, Omid David Tabibi wrote: >> >>>In his article "PEASANT: An endgame program for kings and pawns", Newborn >>>writes: "Position 70 would require a 30-ply search (25,000 hours)" >> >>I did the experiment. A search without transposition tables, without >>pruning/extensions and with material only eval (I forgot, if I used qsearch or >>not). A pawn capture was found at depth 26 (after 8 hours, IIRC). > >I assume you mean depth=26, not ply=26? IE white wins the pawn and I had >thought that this happens on ply=27, which means the first ply of q-search. Correct. Also, I used a qsearch in that experiment. >I will try to run this myself as it would be nice to know exactly how deep this >is precisely, verified by multiple programs... > > >> With hash, it >>is almost guaranteed, that you find it at lower depth. Every second ply, you >>will have to search all moves, and many inferior moves will be refuted by seeing >>the pawn capture earlier. These refutations will be in the HT, and will be >>grabbed in the other more decent lines, to find the solution at lower depth. >> >>For my engine, even 1000 entries in the HT is enough, to solve the problem in >>practically no time. > >Theoretically if you search a perfectly ordered tree, the hash table should not >let you solve it at a shallower than normal depth, although it should cut the >time dramatically as we all see... I don't agree here. See my argument, that every second ply, you have to search all moves, and that this will help you, to find abbrevations (especially, or perhaps only, when using fail soft search). I did another experiment. Again with material only eval, this time with TTs. I disabled repetition detection for that experiment (because they don't play a role when you can win, really, and because they can introduce things more difficult to interprete - as we both know TTs don't handle them correctly in general). The move was found at depth 23 with score of a pawn winning with my normal move ordering (which will be worse in this experiment, because of material only evaluation, than normally). When I changed the move ordering to really random ordering, the solution was found at depth 26 (but still rather fast). Regards, Dieter
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