Author: Will Singleton
Date: 22:32:34 12/03/99
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On December 04, 1999 at 00:17:16, Peter McKenzie wrote: >On December 03, 1999 at 21:12:23, Robert Hyatt wrote: > >>On December 03, 1999 at 18:10:03, Will Singleton wrote: >> >>>On December 03, 1999 at 08:49:19, Andrew Williams wrote: >>> >>>>Over the last few days, I have been fascinated by the discussions on CCC >>>>about positional sacrifices. Some of the discussion has centred on the value >>>>assigned to the attack that is obtained after the sacrifice and I was wondering >>>>how other programs evaluated the position after Hossa's sac: >>>> >>>>r3q1k1/ppp1rp2/2n1b2Q/8/2P5/3B4/PPP2RPP/5RK1 b - - 0 2 >>>> >>>>This is after 1. Bxh6 gxh6 2. Qxh6 from the original position posted by >>>>Peter McKenzie. PostModernist's static evaluation of the position is presented >>>>below. Essentially, it thinks that White is winning by 0.71. The ATTACKTOTAL >>>>score is generated by analyzing the squares around the King to see how many of >>>>them are attacked and what sorts of pieces are attacking them. Please note that >>>>not all the factors that contribute to PM's score are included in the output >>>>below. >>>> >>>>Could other programmers post similar information? I believe that even an >>>>overall static evaluation would be interesting. >>>> >>>>Cheers >>>> >>>>Andrew Williams >>>> >>>> >>>> >>>>SCORE ANALYSIS >>>>BLACK to move >>>> >>>>MATERIAL -137 (Positive means WHITE has more material) W:19086 B:19223 >>>>Game stage M >>>>Actual moves played: 1 (halfMoves=1) >>>> >>>>Fifty move counter: 0 >>>> >>>>r=547 # # # q=1040 # k=15939 # >>>> >>>>o=103 o=106 o=103 # r=565 o=94 # # >>>> >>>> # # n=346 # b=346 # # Q=1022 >>>> >>>> # # # # # # # # >>>> >>>> # # P=101 # # # # # >>>> >>>> # # # B=344 # # # # >>>> >>>>P=103 P=103 P=98 # # R=553 P=103 P=115 >>>> >>>> # # # # # R=555 K=15993 # >>>> >>>> >>>>HCW=1 HCB=1 >>>>cannotCW=1 cannotCB=1 >>>>CCRW=0 CCRB=0 >>>> >>>>Piece Bonuses White=4 Piece Bonuses Black=-34 >>>> >>>>KINGEXPOSURE WHITE=3 KINGEXPOSURE BLACK=16 >>>>DANGERSQUARES WHITE=0 DANGERSQUARES BLACK=5 >>>>ATTACKINGFORCE WHITE=21 ATTACKINGFORCE BLACK=0 >>>>ATTACKTOTAL WHITE=240 ATTACKTOTAL BLACK=0 >>>> >>>> >>>>EVALUATION : 71 (positive means WHITE is winning) >>> >>>For Amateur: >>> >>>r3q1k1/ppp1rp2/2n1b2Q/8/2P5/3B4/PPP2RPP/5RK1 b - - >>> >>>Using a static eval, I get different results if it is White or Black doing the >>>evaluating. I guess this is a result of my asymmetrical king-safety. >>> >>>White says +0.73, Black says +1.29 (+ is good for white). Does anyone else do >>>this asymetrically? >>> >>>Will >> >> >>I have always been asymmetric except for a few failed attempts scattered along >>the way... I think it is the right way myself... > >I have never been asymmetric, unless you count a small bonus for the side to >move. > >I can see certain practical advantages to an asymmetric evaluation, but in the >long term I personally don't think it is a good idea. I'm interested in my eval >being as accurate as possible. If my eval thinks my opponent's sacrificial >attack is unsound then I'm happy to allow the attack even if it means getting >mated from time to time. If I do get mated, then I can learn from it and >improve the eval so it understands that type of position better. > >This approach is in contrast to asymmetric evaluation. Here, if the 'real' >(pre-asymmetry) eval thinks an opponent's sacrificial attack is unsound the >program may still avoid the attack because the 'fudge factor' will be applied to >the eval which may make the attack appear sound. Sure, this allows you to avoid >getting mated from time to time but at what cost? I don't like it for 2 >reasons: > >1) the program will make other concessions to avoid unsound attacks >2) it is harder to improve the accuracy of the evaluation function because the >fudge factor means the eval isn't 'putting itself on the line'. > >I view this issue as similar to penalising blocked positions. I don't like that >because it isn't related to the objective assessment of the position. I don't >mind if humans win the odd game from blocked positions vs my program, as I will >examine those games and improve the play of the program in that type of >position. Also I don't want my program choosing a bad open position instead of >a good closed one (this is a bit extreme, but you get my idea). > >Just my personal philosophy regarding computer chess... > >cheers, >Peter Good points. For me, it turns out the "making the eval as accurate as possible" is an elusive goal, when it comes to king-safety. And since I can't see 15 ply, asymmetry offers an intuitive way to avoid trouble. That is, protecting my king is more important than launching a speculative kside attack. I even think that my asymmetry isn't large enough. I will rarely launch an unwarranted attack, but often will succumb to speculative attack (or rather, fail to take defensive measures in time to avoid sound attacks). I would argue that in theory, your approach is correct. But in practice, given the limits of search, asymmetry is more practical. Will
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