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New version chess engines: CalvinChess 4.2.0 (java)

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Calvin Chess - java chess engine
Author:Dan Kelsey

v.4.2.0:
Calvin 4.2.0 brings a strength increase of around 80 elo, with improvements in a few areas, in particular evaluation and move ordering.

It features a new neural net, with an increased hidden layer size of 384 trained on 470 million positions - as well as eval scaling based on the remaining material on the board. For move ordering, 1-ply conthist has been added, along with a complete re-write of the MovePicker and HistoryTable code.

The primary reason for this release though is to fix a bug that was discovered during CCRL matches, where Calvin would hang when sent a negative time by the match runner. This is apparently a common issue, and so I'm joining a long list of devs who have scrambled to fix it 😄

LTC: Elo difference: 80.6 +/- 23.9
STC: Elo difference: 82.1 +/- 23.4
Estimated strength: 3200

⚖️ Evaluation
New net: 384 HL size, 470m fens (#108)
Material eval scaling (#72)
Optimise NNUE inference / accumulator updates (#73)
🔢 Move ordering
1-ply conthist (#97)
Apply malus to all quiets that don't raise alpha (#83)
Clear ply + 1 killers every node (#80)
🔍 Search
Use improving heuristic in RFP (#79)
Add fail-high aspiration depth reduction (#82)
Use fail-soft in quiescence (#89)
Tweak LMR (#93)
Quiescence search futility pruning (#95)
⌛ Time management
Node TM (#106)
🐛 Bugfix
Fix negative time CCRL bug (#98)
Stop calling movegen twice when in check (#71)
How to run
Please download one of the jar files from this release. There are two release jars: calvin-chess-engine and calvin-chess-engine-no-simd. The no-simd release is specifically for CCRL testers: since ChessGUI does not support passing Java opts to a jar file, the Vector API which Calvin uses for NNUE must be disabled.

For the standard calvin-chess-engine release, Calvin can be started by running the command:

java --add-modules jdk.incubator.vector -jar path/to/calvin-chess-engine-4.2.0.jar

For the CCRL calvin-chess-engine-no-simd release, the Java opt can be ommited:

java -jar path/to/calvin-chess-engine-no-simd-4.2.0.jar

CalvinChess 4.2.0 download


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