Author: Omid David Tabibi
Date: 15:19:06 10/13/03
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On October 13, 2003 at 08:08:15, Omid David Tabibi wrote: >On October 13, 2003 at 07:51:47, Tony Werten wrote: > >>On October 13, 2003 at 04:47:28, Omid David Tabibi wrote: >> >>>On October 13, 2003 at 02:28:46, Tony Werten wrote: >>> >>>>On October 12, 2003 at 07:35:57, Omid David Tabibi wrote: >>>> >>>>>On October 12, 2003 at 07:24:51, Uri Blass wrote: >>>>> >>>>>>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. >>>>>>> >>>>>>>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. >>>>>> >>>>>>How can checks only in the first ply of the quiescence >>>>>>do your program more than twice slower in nodes per second? >>>>>> >>>>>>Did you profile your program to see what parts it waste more time on them? >>>>> >>>>>Falcon's quiescence uses SEE to prune losing captures. Also its gen_captures() >>>>>function is very fast because of the attack tables. But adding checks requires >>>>>generation of all moves (a costly operation), and doing a makemove() for each of >>>>>them to see whether they check the opponent (makemove is the most expensive >>>>>function in the program, since the attack tables are dynamically updated there). >>>>>And considering that more than 75% of the nodes in a normal search are in >>>>>quiescence, and most of those nodes are at depth = 0 (i.e., the first ply of >>>>>quiescence), no wonder that the slowdown is so steep. >>>>> >>>>>I can optimize this a little by using a gen_checking_moves() function, instead >>>>>of generating all moves, but the slowdown will remain significant even in that >>>>>case. >>>> >>>>Nope, not if you do it right. >>>> >>>>You already have done the hard work, why not use it ? >>>> >>>>Take the position of the opponent king, generate all knight moves from that >>>>square, look in your attacktables if you attack these squares with a knight. >>>> >>>>If yes, you have a knight checkmove. >>>> >>> >>>I was thinking about this overnight, and this seems to be a good way of doing >>>it. Starting from the king's square I should scan all diagonals, columns and >>>ranks, until reaching a blocking piece. >> >>Yes, except that if the piece is of color "side to move", you should continue >>the scan. > >Ah yes, discovered checks! And also weird cases involving ep: [D]8/8/8/1k1pP1R1/8/8/8/4K3 w - d6 0 2 The move exd6 is a checking move. sigh... > > >> >>Tony >> >>>For each such square check whether an >>>appropriate piece atacks it. Knight checks can be generated as you mentioned. >>> >>> >>> >>>>Tony >>>> >>>>> >>>>> >>>>>> >>>>>>My experience when I first tried was better result in test suites when there was >>>>>>not significant change in the level in games. >>>>>> >>>>>>I decided to keep it because I knew that my implementation is not optimal and I >>>>>>may earn later by pruning some of the checks. >>>>>> >>>>>>I later discovered bugs in my implementation that I fixed(for example returning >>>>>>wrong mate scores from the quiescence) >>>>>> >>>>>>I also decided later to prune part of the checks in the qsearch when the >>>>>>attacker can be captured and is not defended. >>>>>> >>>>>>I did not compare last version with no checks in the quiescence. >>>>>> >>>>>>Uri
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