Chess engine: Arcanum 2.1 NNUE

Arcanum is a free UCI chess engine under the MIT license.

Rating Chess Engines Diary CEDR=2922

v.2.1:

Changes

Use vertically symmetric mirroring for feature indices in the NNUE.

Fix an issue with the NNUE backpropagation, where the WDL result target for black was not set correctly.

A new NNUE net trained with the changes above.

The v1 net from Arcanum 2.0 and v2 net from Arcanum 2.1 is thus not interchangeable

Added reporting of seldepth in uci.

Small rework of time management to use more time early, and be more conservative in the endgame.

Added MoveOverhead UCI option, to enable adding a millisecond margin to the time usage. Default is 10ms.

Fix an issue where a null move was returned by search if it did not have enough time to search any moves.

Arcanum is now forced to return a legal move

Other bugfixes to enable compiling and running on Linux.

Elo estimates

Arcanum 2.1 is estimated to be ~200 Elo stronger than Arcanum 2.0. See results below

Self play

Time control: 10s + 0.1s

Score of v2.1 vs v2.0: 141 - 16 - 43 (Win - Loss - Draw)

v2.1 playing White: 70 - 9 - 21

v2.1 playing Black: 71 - 7 - 22

Elo difference: 254.7 +/- 50.3, LOS: 100.0 %, DrawRatio: 21.5 %

Time control: 60s + 0.5s

Score of v2.1 vs v2.0: 125 - 21 - 54 (Win - Loss - Draw)

v2.1 playing White: 64 - 14 - 22

v2.1 playing Black: 61 - 7 - 32

Elo difference: 200.2 +/- 45.1, LOS: 100.0 %, DrawRatio: 27.0 %

Arcanum 1.11.1 - results

Arcanum 2.1 download

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