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| Subject: Latest abrok Development Version November 21st 2021 (SF The gift that keeps on giving Mon Nov 22, 2021 10:06 am | |
| or Haswell CPUs Windows x64 for modern computers + AVX2 Windows x64 for modern computers Windows x64 + SSSE3 Windows x64 Linux x64 for Haswell CPUs Linux x64 for modern computers + AVX2 Linux x64 for modern computers Linux x64 + SSSE3 Linux x64 | Author: Stéphane Nicolet Date: Sun Nov 21 21:18:08 2021 +0100 Timestamp: 1637525888 Introduce Optimism Current master implements a scaling of the raw NNUE output value with a formula equivalent to 'eval = alpha * NNUE_output', where the scale factor alpha varies between 1.8 (for early middle game) and 0.9 (for pure endgames). This feature allows Stockfish to keep material on the board when she thinks she has the advantage, and to seek exchanges and simplifications when she thinks she has to defend. This patch slightly offsets the turning point between these two strategies, by adding to Stockfish's evaluation a small "optimism" value before actually doing the scaling. The effect is that SF will play a little bit more risky, trying to keep the tension a little bit longer when she is defending, and keeping even more material on the board when she has an advantage. We note that this patch is similar in spirit to the old "Contempt" idea we used to have in classical Stockfish, but this implementation differs in two key points: a) it has been tested as an Elo-gainer against master; b) the values output by the search are not changed on average by the implementation (in other words, the optimism value changes the tension/exchange strategy, but a displayed value of 1.0 pawn has the same signification before and after the patch). See the old comment https://github.com/official-stockfish/Stockfish/pull/1361#issuecomment-359165141 for some images illustrating the ideas. ------- finished yellow at STC: LLR: -2.94 (-2.94,2.94) <0.00,2.50> Total: 165048 W: 41705 L: 41611 D: 81732 Elo +0.20 Ptnml(0-2): 565, 18959, 43245, 19327, 428 https://tests.stockfishchess.org/tests/view/61942a3dcd645dc8291c876b passed LTC: LLR: 2.95 (-2.94,2.94) <0.50,3.00> Total: 121656 W: 30762 L: 30287 D: 60607 Elo +1.36 Ptnml(0-2): 87, 12558, 35032, 13095, 56 https://tests.stockfishchess.org/tests/view/61962c58cd645dc8291c8877 ------- How to continue from there? a) the shape (slope and amplitude) of the sigmoid used to compute the optimism value could be tweaked to try to gain more Elo, so the parameters of the sigmoid function in line 391 of search.cpp could be tuned with SPSA. Manual tweaking is also possible using this Desmos page: https://www.desmos.com/calculator/jhh83sqq92 b) in a similar vein, with two recents patches affecting the scaling of the NNUE evaluation in evaluate.cpp, now could be a good time to try a round of SPSA tuning of the NNUE network; c) this patch will tend to keep tension in middlegame a little bit longer, so any patch improving the defensive aspect of play via search extensions in risky, tactical positions would be welcome. ------- closes https://github.com/official-stockfish/Stockfish/pull/3797 Bench: 6184852 see source |
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