Stockfish 2023071120 NNUE for Windows and Linux, compiled by Joost VandeVondele (Elo -2,35!)

- July 14, 2023

Stockfish 2023071120 - UCI chess engine, compiled by AndrovT
Rating CEDR=3732

Timestamp: 1689109009

Remove classical evaluation

since the introduction of NNUE (first released with Stockfish 12), we have maintained the classical evaluation as part of SF in frozen form. The idea that this code could lead to further inputs to the NN or search did not materialize. Now, after five releases, this PR removes the classical evaluation from SF. Even though this evaluation is probably the best of its class, it has become unimportant for the engine's strength, and there is little need to maintain this code (roughly 25% of SF) going forward, or to expend resources on trying to improve its integration in the NNUE eval.

Indeed, it had still a very limited use in the current SF, namely for the evaluation of positions that are nearly decided based on material difference, where the speed of the classical evaluation outweights its inaccuracies. This impact on strength is small, roughly 2Elo, and probably decreasing in importance as the TC grows.

Potentially, removal of this code could lead to the development of techniques to have faster, but less accurate NN evaluation, for certain positions.

STC

https://tests.stockfishchess.org/tests/view/64a320173ee09aa549c52157

Elo: -2.35 ± 1.1 (95%) LOS: 0.0%

Total: 100000 W: 24916 L: 25592 D: 49492 Elo -2.35

Ptnml(0-2): 287, 12123, 25841, 11477, 272

nElo: -4.62 ± 2.2 (95%) PairsRatio: 0.95

LTC

https://tests.stockfishchess.org/tests/view/64a320293ee09aa549c5215b

Elo: -1.74 ± 1.0 (95%) LOS: 0.0%

Total: 100000 W: 25010 L: 25512 D: 49478 Elo -1.74

Ptnml(0-2): 44, 11069, 28270, 10579, 38

nElo: -3.72 ± 2.2 (95%) PairsRatio: 0.96

VLTC SMP

https://tests.stockfishchess.org/tests/view/64a3207c3ee09aa549c52168

Elo: -1.70 ± 0.9 (95%) LOS: 0.0%

Total: 100000 W: 25673 L: 26162 D: 48165 Elo -1.70

Ptnml(0-2): 8, 9455, 31569, 8954, 14

nElo: -3.95 ± 2.2 (95%) PairsRatio: 0.95

closes https://github.com/official-stockfish/Stockfish/pull/4674

Bench: 1444646

Stockfish rating progress:

Engine	Rating	Score	Games	(%)
Stockfish 20230227	3732.4	92.00	134	68.66
Stockfish 241022	3724.2	64.00	112	57.14
Stockfish 031022	3720.9	110.50	158	69.94
Stockfish 070922	3718.9	123.00	164	75.00
Stockfish 20230325	3718.5	109.00	169	64.50
Stockfish 20221107	3717.8	106.50	186	57.26
Stockfish 20230308 Ivec	3717.6	79.00	120	65.83
Stockfish 301022	3717.6	112.00	175	64.00
Stockfish 20230218	3715.1	110.50	164	67.38
Stockfish 20230128	3713.1	69.00	106	65.09
Stockfish 290522 Ivec	3711.0	113.00	144	78.47
Stockfish 080622 Ivec	3709.7	94.50	133	71.05
Stockfish 161022	3709.5	147.00	240	61.25
Stockfish 20221123	3709.5	247.50	356	69.52
Stockfish dev-20230520	3708.9	106.50	174	61.21
Stockfish 20221224	3707.4	65.50	104	62.98
Stockfish dev-20230503 Ivec	3706.8	168.50	234	72.01
Stockfish 101022 Ivec	3705.6	82.50	138	59.78
Stockfish 20230308	3705.2	167.00	259	64.48
Stockfish 040722	3705.0	308.50	433	71.25
Stockfish 20230114	3704.6	295.00	410	71.95
Stockfish 20230314	3704.6	119.50	200	59.75
Stockfish 20221221	3703.6	165.00	267	61.80
Stockfish 061122 Ivec	3703.2	130.00	201	64.68
Stockfish 20230314 Ivec	3701.2	94.00	137	68.61
Stockfish dev-20230505	3700.7	97.50	172	56.69
Stockfish 20230104	3700.7	95.50	151	63.25
Stockfish 170922 Ivec	3700.2	107.50	155	69.35
Stockfish 130722	3698.9	102.50	166	61.75
Stockfish 20221120	3698.6	134.50	203	66.26
Stockfish 20230125	3698.5	136.50	201	67.91
Stockfish 110722 Ivec	3698.3	105.50	134	78.73
StockfishMZ 170522	3697.7	345.00	482	71.58
Stockfish 20230101	3697.5	74.00	119	62.18
Stockfish 070622	3697.1	279.00	462	60.39
Stockfish 060822 Ivec	3696.4	96.50	153	63.07
Stockfish 081022	3696.1	89.50	176	50.85
Stockfish dev-20230503	3692.7	78.50	110	71.36
Stockfish 15	3691.1	1038.00	1623	63.96
Stockfish 20221209	3690.4	122.50	192	63.80
Stockfish 030522	3689.6	101.50	150	67.67
Stockfish 20230329	3688.5	75.00	132	56.82
Stockfish 20230202	3687.0	86.00	128	67.19
Stockfish 20221220	3684.4	61.00	107	57.01
Stockfish 20230313	3683.6	82.50	104	79.33
Stockfish 170922	3678.1	150.00	226	66.37
StockfishMZ Iccf 240522	3637.8	100.50	150	67.00