Author: Tony Werten
Date: 04:51:47 10/13/03
Go up one level in this thread
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. 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.