Author: Vincent Diepeveen
Date: 05:50:12 10/13/03
Go up one level in this thread
On October 12, 2003 at 12:03:37, Omid David Tabibi wrote: >On October 12, 2003 at 11:45:07, Tord Romstad wrote: > >>On October 12, 2003 at 10:23:35, Omid David Tabibi wrote: >> >>>[D]6k1/5p2/3P2p1/7n/3QPP2/7q/r2N3P/6RK b - - 0 1 >>> >>>If you do checks everywhere in quiescence, you should see this immediately. >> >>If I did *all* checks everywhere in qsearch, I should see it instantly, yes. >>But as you >>remarked in the article at the beginning of this thread, this is too expensive. >>Beyond >>the first ply of qsearch, I have very strong restrictions about when and which >>checks >>to generate. >> >>>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! >> >>I do repetition detection in quiescence, and I have no max extension limit. >>Looking >>closer on the position in question, it does seem a bit strange that I need such >>a long >>time to find the solution. The combination is not very deep. Perhaps I have a >>bug >>somewhere -- it's worth a closer look. >> >>>Falcon doesn't manage to solve number 12 either. >> >>Number 12 is very hard. But even solving number 10 and 11 in less than a >>second >>is very impressive, IMHO. >> >>>>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()... >> >>I am not so sure about that. Most of what you write above applies to my engine, >>too. The attack tables are useful when generating checks, too. And of course >>you >>do not generate checks before you have generated and searched all captures and >>they all failed low. >> >>>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. >> >>This sounds extremely dangerous to me -- doesn't this imply that you will not >>always detect mates in qsearch? > >No checkmate can possibly take place at the first ply of quiescence, since I do >the following in the main search: > >... >makemove(move); >if (other side is in check) > extension += 1; >call_depth = depth - 1 + extension; >if (call_depth > 0) > score = -search(..., call_depth); >else > score = -quiescence(...); >... isn't that very inefficient unless you extend moves that give a check instead of moves that get out of check. of course moves that get out of check, to extend them is always better which is easily provable even theoretically. >So if the other side is in check the depth will be extended instead of calling >quiescence. > >But within the quiescence no checkmate can be detected in the normal version. > > >>And doesn't this cause too many tactical mistakes? > >It to causes problems mainly in null-move pruning. Assume you are at depth = 3 >and use R = 2. Your calling depth is 3-2-1=0, i.e., you directly call quiescence >(after doing a null-move). Now it is the opponent's turn who checkmates you in >the first ply of quiescence. Using checks in quiescence the checkmate will be >detected, which will trigger a mate threat extension in the main search. >Otherwise (in the normal version) just eval() is returned and assuming it is >above beta we have a fail-high. All good and nice we are sure that our position >is good enough to justify a cutoff, while in fact we are mate in 1! > >That's the main reason why checks in the first ply of quiescence contribute so >much to tactical strength. > > >> >>>>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... >> >>Very interesting. >> >>>>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. >>> >>>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. >> >>This is very possible. I have experimented with values of R below 3, and with a >>minimalistic qsearch without checks, but never in combination. Probably yet >>another thing I should try ... >> >>Tord
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