Author: Uri Blass
Date: 08:06:01 10/12/03
Go up one level in this thread
On October 12, 2003 at 10:49:44, Omid David Tabibi wrote: >On October 12, 2003 at 08:26:54, Uri Blass wrote: > >>On October 12, 2003 at 08:21:35, Uri Blass 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). >>> >>> >>>My attack tables are also dynamically updated in makemove but >>>when I generate checks I do not make moves that are not checks and I use the >>>from and to square to define if the move is a check. >>> >>>If you do makemove for moves that are not checks only to see if they check the >>>opponent(this is what I understand from your post) it seems that you spend a lot >>>of time on unnecessary moves. >>> >>>You should check if they check the opponent without makemove or have a special >>>function to generate only checks like you suggest later. >>> >>>I do not see why it is not going to reduce most of your slow down in nodes per >>>second. > >Because I will have to generate all moves anyway. It will eliminate the overhead >of unecessary makemove() for each of those moves, but the overhead of >gen_non_caps() will still be there. I assumed that the main overhead is because of unnecessary makemove and not because of gen_non_cap() based on the following words of you: "makemove is the most expensive function in the program, since the attack tables are dynamically updated there" Uri
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