Arcanum is a free UCI chess engine under the MIT license.
Author:Lars Aurud, Rating Chess Engines Diary CEDR=2922
v.2.4:
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Add Internal Iterative Reductions (IIR)
Remove Futility Pruning.
Add Singular Extension.
Add ProbCut
Avoid RFP, NMP, Razoring and LMP in PV nodes
Reduce LMR search more in expected cutnodes.
Rework the history heuristic from being relative to use the history gravity function.
Fix some issue in SEE where the wrong result was returned
New attacker are now added correctly when blocking pieces move
Add support for non-capture SEE
Use SEE to order captures
Add counter move heuristic to move ordering
Performance
Add more TT prefetches
Optimize some element-wise calculations in NNUE training
Remove memory allocations in the NNUE training loop
Other
Add support for incbin, embedding the default NNUE net in the executable.
Improve code quality of FEN parser.
Fix an issue when reporting scores found in syzygy which were affected by the NormalizeScore option
Elo Estimate
Arcanum v2.4 is estimated to be ~112 Elo stronger than Arcanum v2.3.1 based on self play.
Self Play
Time Control 120s + 1s
Score of v2.4 vs v2.3.1: 111 - 17 - 172 (Win - Loss - Draw)
v2.4 playing White: 68 - 5 - 77
v2.4 playing Black: 43 - 12 - 95
Elo difference: 112.7 +/- 25.0, LOS: 100.0 %, DrawRatio: 57.3 %
Arcanum 2.3.1 - results
| Opponent | score | +- | Games |
| Ifrit 4.3 JA | 8/8 | +8 | 8 Games |
| Skiull 0.6 | 8/8 | +8 | 8 Games |
| ChandraChess 2.0 | 3/8 | -2 | 8 Games |
| Molybdenum 4.1 | 1/8 | -6 | 8 Games |
| Elixir 3.0 JA | 0.5/8 | -7 | 8 Games |
| Prophet 4.4 | 6/6 | +6 | 6 Games |
| ChandraChess 2.0 JA | 2.5/6 | -1 | 6 Games |
| Critter 1.6a | 1.5/6 | -3 | 6 Games |
| Lizard 11.1 | 0/6 | -6 | 6 Games |
| LazySMP 5.0 | 4/4 | +4 | 4 Games |
| LazySMP 4.0 | 4/4 | +4 | 4 Games |
| Zangdar 2.31 | 2.5/4 | +1 | 4 Games |
| CalvinChess 5.0.1 | 1.5/4 | -1 | 4 Games |
| CalvinChess 5.0.2 | 0.5/4 | -3 | 4 Games |
| Velvet 8.1.1 | 0/4 | -4 | 4 Games |
| Barbarossa 0.7.0 | 2/2 | +2 | 2 Games |
| Toad 1.4.0 | 2/2 | +2 | 2 Games |
| Floyd 0.9 JA | 2/2 | +2 | 2 Games |
| Knightx 4.2 | 2/2 | +2 | 2 Games |
| Toad 1.2.0 | 2/2 | +2 | 2 Games |
| Prometheus 0.2 JA | 2/2 | +2 | 2 Games |
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