Author: Omid David Tabibi
Date: 05:56:05 10/13/03
Go up one level in this thread
On October 13, 2003 at 08:50:12, Vincent Diepeveen wrote: >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. Sure. There is no difference. > >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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