Author: Vincent Diepeveen
Date: 08:49:02 10/12/03
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On October 12, 2003 at 06:32:25, Omid David Tabibi wrote: >Recently I conducted some extensive experiments with two versions of Falcon, one >with checks in quiescence and one without. Falcon already has lots of >extensions, but adding checks in quiescence resulted in a significant boost for >tactical strength. > >I tested the following options: > >a) checks everywhere in quiescence >b) checks only in the first ply of quiescence >c) no checks in quiescence > >Option 'a' was ruled out after some testing, as it resulted in a total explosion >of quiescence search. I tried controlling it in some ways, but still the >overhead was considerably more than the benefit. It seems that The King and >HIARCS are the only engines using this method. +diep +rebel? >Option 'b' produces almost the same tactical strength as option 'a', with a >considerably lower overhead. The most significant contribution of checks in the >first ply of quiescence seems to be in conjuction with null-move pruning near >leaf nodes: > >For example at depth = 3, using R = 2, the null-move search will be called with >a depth of 0, i.e., direct call to quiescence search. Here the presence of >checks in the first ply can return a checkmate value which will result in an >extension to main search (mate threat extension). > >Only using checks in the first ply of quiescence, Falcon managed to solve almost >all tactical positions of LCTII in less than 1 second, outperforming the normal >version (no checks in quiescence). But adding checks in quiescence (although >only at its first ply) significantly slowed down the engine (from average of >350kNPS to 150kNPS on my PIII/733MHz) and resulted in a worse branching factor. > >Next I conducted some self-play matches between the two versions, and also some >matches versus other engines. > >The results of the matches were quite interesting. The version with checks in >quiescence not only didn't outperform the normal version in actual games, but >produced slightly inferior games in general. I especially conducted a few tens >of matches for each version against Crafty. The normal version beat Crafty by >something like 60%-40%. The version with checks in quiescence scored 50%. >Whenever the game turned tactical it literally butchered Crafty, but on normal >quiet positions Crafty once and again made a mincemeat of it by simply searching >deeper, which resulted in a better positional play. > >So, it seems that adding checks in quiescence is great for solving tactical test >suites, but not so for actual game play. The same goes for some of the >aggressive extensions I tried; great for tactics, poor in games. > >I'd be interested to hear others' thoughts on this issue. > >I also considered using some form of static mate threat detection, independent >of null-move search, but haven't found any interesting way to do so yet. Also, >Falcon does not detect checkmates statically in eval(), but only when one side >doesn't have any legal moves, i.e., it needs an additional ply to see the >checkmate. But I don't think the latter is any important, since when the other >side is checked, a check extension is already done, which will result in the >detection of the checkmate.
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