Author: Tony Werten
Date: 23:53:04 10/13/03
Go up one level in this thread
On October 13, 2003 at 18:19:06, Omid David Tabibi wrote: >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... Skip it. Tony > > > >> >> >>> >>>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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