Author: Omid David Tabibi
Date: 04:17:27 10/14/03
Go up one level in this thread
On October 14, 2003 at 04:46:19, Omid David Tabibi wrote: >On October 14, 2003 at 04:22:48, Christophe Theron wrote: > >>On October 14, 2003 at 02:53:04, Tony Werten wrote: >> >>>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 >> >> >> >>Yes. Do yourself a favor and ignore this case. You will *NEVER* notice the >>difference. >> > >Ah yes, ep checking captures can be totally ignored in quiescence, since they >will be generated anyway as part of non-losing captures... Actually it seems that it is safe to ignore all capturing checks altogether in gen_checks(). If the capture is non-losing, it will already be generated, and if it is a losing capture, the odds that it turns out to be a good move aren't that high (assuming that SEE hasn't mistakenly deemed the move as losing capture, while in fact it is a winning capture since one of the defenders is pinned...) > > >> >> >> Christophe
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