Author: Uri Blass
Date: 09:01:24 10/12/03
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On October 12, 2003 at 11:49:49, Omid David Tabibi wrote: >On October 12, 2003 at 11:13:22, Andrew Williams wrote: > >>On October 12, 2003 at 10:45:36, Omid David Tabibi wrote: >> >>>On October 12, 2003 at 08:25:27, Andrew Williams 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). >>>> >>>>Hi Omid, >>>> >>>>I have a move_gives_check_or_promotes(move mv) function which I use in certain >>>>places (there's an associated gives_discovered_check(..)). At the time >>>>implemented it, this was a lot faster than doing the make_move(..), for the same >>>>reasons that you give. However, I'm afraid I can't remember exactly how much >>>>faster. Do you have a get_me_out_of_check() move generator, for the case when >>>>the King is in check? Or do you just generate (and make) all moves again if the >>>>King is in check in the Qsearch? >>> >>>Generate all moves and do makemove() in an inefficient way... >>> >> >>My get_me_out_of_check() function generates captures of the attacking piece, >>then if it's a sweeper it walks between king and attacker generating blocking >>moves. Finally it looks at the King's escape squares to see if they are >>clear/attacked. The nice thing about this is that you can use your attackboards >>to do lots of this work. The nasty thing is that if you use it in the normal >>search, you run the risk of appalling losses until you iron out all the bugs. >>Caveat emptor (I don't know what "user of a technique" is in Latin). > >Good idea. Will try to implement it tonight, but it would be hard to debug since >I cannot compare the new nodes count to the old one as the order of moves will >change using the new check evasion move generator. Using this move generator >also helps in knowing the exact number of legal moves, which can be used for one >reply extension. I think that you should use the perft function for debugging. the result of perft is not dependent in the order of moves and I used it for debugging in every time that I changed my move generator. Uri
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