Author: Vincent Diepeveen
Date: 08:57:02 10/12/03
Go up one level in this thread
On October 12, 2003 at 10:23:35, Omid David Tabibi wrote: >On October 12, 2003 at 09:27:09, Tord Romstad 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. >> >>These are not the only ones. I am fairly sure Diep searches checks everywhere >>in the >>qsearch, and Gothmog (my engine) also does. > >True, I referred to commercial engines. HIARCS and King definitely do checks >everywhere in quiescence (with certain limitations of course), but I'm not >completely sure about Fritz, Shredder, and Tiger (Junior seems not to have a >quiescence at all, but it has a large set of extensions). > > >> >>>Option 'b' produces almost the same tactical strength as option 'a', with a >>>considerably lower overhead. >> >>Interesting. I have only tried options 'a' and 'c' myself, and always found >>option >>'a' to be significantly better (in games as well as test suites). I should >>probably >>do some experiments with option 'b' as well. >> >>>Only using checks in the first ply of quiescence, Falcon managed to solve almost >>>all tactical positions of LCTII in less than 1 second, >> >>Very impressive. Gothmog (on an Athlon XP 2.4 GHz) solves the first 8 positions >>in >>less than a second, but needs 1:18 for number 9, > >[D]6k1/5p2/3P2p1/7n/3QPP2/7q/r2N3P/6RK b - - 0 1 > >If you do checks everywhere in quiescence, you should see this immediately. >After 1...Rxd2 2.Qxd2 all the rest of the moves are checks until you detect draw >by threefold repetition (maybe you've turned off repetition detection in >quiescence? or your max extensions limit is too shallow...). HIARCS finds the >move at the first iteration! > >The following is Falcon's analysis (with checks enabled only at the first ply of >quiescence): > >Falcon 0.0.3.5 running on GenuineIntel 733MHz 256MB: >depth time nodes nps score variation > 6/10 0.16 16k 103k 3.22 1...h5f4 > 6/12 0.29 30k 104k 8.55 1...f7f5 1.d6d7 a2a8 2.d4d5 > 6/12 0.31 32k 106k 3.47 1...h5f4 1.d6d7 f4e6 2.d7d8q e6d > 3.d4d8 g8h7 > 8/14 0.43 47k 109k 3.61 1...h5f4 1.d6d7 f4e6 2.d7d8q e6d > 3.d4d8 g8h7 4.d8d4 > 8/17 0.89 99k 111k 3.50 1...a2d2 1.d4d2 h3f3 2.d2g2 f3f4 > 3.d6d7 f4d6 >10/19 0.97 108k 111k 3.17 1...a2d2 >10/19 11.42 1275k 111k 0.00 1...a2d2 1.d4d2 h3f3 2.g1g2 f3f1 > 3.g2g1 f1f3 >12/21 11.54 1292k 112k 0.00 1...a2d2 1.d4d2 h3f3 2.g1g2 f3f1 > 3.g2g1 f1f3 >14/23 12.04 1374k 114k 0.00 1...a2d2 1.d4d2 h3f3 2.g1g2 f3f1 > 3.g2g1 f1f3 >16/25 14.07 1722k 122k 0.00 1...a2d2 1.d4d2 h3f3 2.g1g2 f3f1 > 3.g2g1 f1f3 > > > >>25 seconds for number 10, 25 >>seconds >>for number 11, and doesn't solve number 12 at all (at least not within a few >>hours). > >Falcon doesn't manage to solve number 12 either. > > >>Earlier >>versions solved number 9 instantly, but the quick solution turned out to be >>caused by >>a bug: I had accidentally changed my single-reply-to-check extension to a >>two-replies-to-check extension. >> >>>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. >> >>You must have a very inefficient way of generating checks, I think. > >That's true. Only recently I added checks in quiescence to the engine, and so >still haven't written a gen_checks() functions. However, the kind of attack >tables I use result in a very speedy generation of captures, which results in a >very optimized captures only quiescence. Adding checking moves will slow down >the engine considerably anyway, even if I write a good gen_checks()... > >One thing I have to mention is that in the normal version I never check for >check evasions in quiescence. If the side to move is in check and doesn't have >any legal non-losing capture, I just return eval(). That's another reason why >the normal quiescence is so fast. > > >>I haven't >>spent a >>lot of time optimising check generation myself, and in my program the NPS drops >>by >>only about 15%. It would probably be possible to push it below 5% with some >>effort. >> >>>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. >> >>It seems like checks in the qsearch is one of those things that works well in >>some >>programs, and not in others. Crafty, for instance, seems to do very well >>without >>any checks whatsoever, > >I wouldn't say so from a tactical point of view. Whenever the game turned >tactical, Crafty didn't have any chance against Falcon with checks in >quiescence. But Crafty did search deeper and played a better positional game. I >must also add that Falcon uses a huge number of different extensions (I think >only HIARCS has more extensions), and so maybe adding checks in quiescence on >top of them all isn't such a good idea... > > >>but for me the results without checks are clearly worse. >> >>Other ideas that I have never been able to make work are recapture extensions >>and >>all sorts of nullmove pruning except plain R=3 (R=2, R=2.5, adaptive pruning and >>verified >>nullmove pruning are all clearly worse for me). > >In Falcon I conducted all the experiments I conducted on Genesis for the paper >verified null-move pruning, and got the same results. Plain R=3 was too risky >neglecting many tactical shots. I now use a modified version of verified >null-move pruning. This simply is a matter of bad experimentation from your side. When you do check first ply in qsearch and no dubious forward pruning last ply (your search depths are *very* big considering hardware) then at your 'testset' that version will outperform any other version trivially with R=3, because it's nearly all mating problems. >But maybe plain R=3 didn't work for me because I didn't have checks in >quiescence, and so it resulted in a very inaccurate search. The only program >I've heard which uses plain R=3 is DIEP, which does conduct checks everywhere in >quiescence. You should test R=3/2 too when you forward prune that much. > >> >>>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. >> >>I have also experimented with static mate threat detection in the evaluation >>function, >>but it is very tricky to get it right. Also, all minor bugs are likely to have >>catastrophic >>consequences (at least if you allow the evaluation function to return a mate >>score when >>the static mate finder reports a mate in n for the side to move). >> >>Tord
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.