Author: Uri Blass
Date: 08:33:38 10/12/03
Go up one level in this thread
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). I also have a similiar function and it was from the beginning of movei. Checks in the qsearch is probably a bad idea without that function. Uri
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