Author: Laurence Chen
Date: 05:04:40 12/05/00
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On December 04, 2000 at 23:27:21, William Penn wrote: >CM8000 - an analysis anomaly > >This is an analysis after 1.Nf3 Nf6 2.c4 c6 3.Nc3 d5 4.e3 e6 5.d4 Nbd7 6.Qc2 Bd6 >7.Be2 0-0 8.0-0 e5 9.cxd5 cxd5 10.Nb5 Bb8 11.dxe5 Nxe5 12.Bd2 Bg4. The position >after 12...Bg4 is as follows: > >BR BB -- BQ -- BR BK -- >BP BP -- -- -- BP BP BP >-- -- -- -- -- BN -- -- >-- WN -- BP BN -- -- -- >-- -- -- -- -- -- BB -- >-- -- -- -- WP WN -- -- >WP WP WQ WB WB WP WP WP >WR -- -- -- -- WR WK -- > >This is a known position with 17 example games found in the literature and >databases. 14 games played 13.Nbd4 which may be considered the book move, 2 >games played 13.Bb4, and 1 game played 13.Rfc1. Nobody tried 13.Nfd4. Using >CM8666 Deep (as described previously, analogous to Shep's CM6666 Deep for >CM6000), analysis yielded the following information in the Thinking Lines >window: > > after 12...Bg4 >Time Depth Score Positions Moves >0:28 9 0.37 1M * Bb4 (* rounded off to nearest 1000) >1:00 10 0.18 3M Bb4 >2:27 10 0.31 8M Nfd4 >5:58 11 0.23 19M Nfd4 >17:31 12 0.14 58M Nfd4 >23:07 12 0.28 78M Bb4 >41.43 13 0.12 142M Bb4 >2:11:00 14 0.13 448M Bb4 > >So my CM personality thinks 13.Bb4 is the best move in this position with a >+0.13 score at 14 ply. It didn't find the book move 13.Nbd4. Why? Well, maybe >the book move isn't as good. To test this theory, I made the book move. If >it's not as good, the resulting analysis should give poorer scores (smaller >positive values) than 13.Bb4. Here's what it shows: > > after 12...Bg4 13.Nbd4 >Time Depth Score Positions Moves >0.16 9 0.56 1M Nxf3+ >0.36 10 0.44 2M Nxf3+ >1:33 11 0.43 5M Nxf3+ >6:00 12 0.37 20M Nxf3+ >17:12 13 0.37 59M Nxf3+ >1:05:00 14 0.29 220M Nxf3+ > >Surprisingly 13.Nbd4 gives higher scores than 13.Bb4. I thought that might be >because the Selective Search was set too high in CM8666 Deep. So I searched >with smaller Selective Search settings (including a setting of zero, among >others) but it still couldn't find the book move, 13.Nbd4. > >Clearly 13.Nbd4 produces better scores, so why wasn't it found and selected as >the best move? This is an unexplained anomaly, and I don't know the answer. >Does anyone? >WP I believe that all chess engines suffer from the Horizon vision, that is, it's not able to see the best move unless it is fed to it, then it changes its evaluation. Perhaps that's the reason why opening books are created to help chess engines play the correct moves for a given position. The CM book is not a very long nor extensive opening book. Regards, Laurence
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