Author: Omid David Tabibi
Date: 05:08:15 10/13/03
Go up one level in this thread
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! > >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
This page took 0.01 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.