Move

Throttle has been rewritten from scratch as Polonium

Throttle Chess Engine

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Throttle is a UCI chess engine developed using Sebastian Lague's chess framework.

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Playing

You can either download my latest version in releases or play with me online at lichess but note I may not always be online. If you choose to download me, also note that I am a UCI chess engine and I don't come with my own graphical interface. I would recommend you to use a GUI to test my engine if you are not familiar with the UCI protocol such as Arena Chess GUI or Banksia Chess GUI.

Lichess

Connected with lichess using this lichess-bot tool.

Rating (Playing strength)

Version	Estimate CCRL Elo	CCRL Blitz	CCRL Bullet	CEDR
3.1	2379.6 +/- 64.2	-	-	-
3.0	2376.3 +/- 62.0	-	-	-

• Estimated Elo is calculated against Stash 14.0 with a tc of 10+0.1(sorry stash!)
• From 3.2 onwards, Elo is calculated against the previous versions of Throttle (because Stash randomly crashes)

Features

Search:

• Aspiration window v2.4 16.6 +/- 9.6
• Fail-Soft Negamax Search
• Quiescence Search
• Principle Variation Search
• Triple PVS v1.5 21.3 +/- 11.1

Pruning:

• Actual TT pruning v2.1 136.4 +/- 31.2
• A/B Pruning
• Null Move Pruning
• Reverse Futility Pruning
• Futility Pruning (depthdepthmargin) v3.0 15.7 +/- 9.2 vs Normal futility pruning
• Quiescence Search Standing Pat Pruning
• Quiescence Search Delta Pruning v2.5 11.7 +/- 7.7
• Mate Distancing Pruning

Reductions:

• Internal Iterative Reduction
• Late move reductions with triple pvs

Extensions:

• Check Extensions

Ordering:

• TT Moves
• MVV-LVA (for good captures)
• Killer moves (quiets)
• History moves (quiets) v2.0 67.9 +/- 20.9

Time Management:

• Hard and Soft Time Management

Evaluation:

• Tuned with Gedimas' Texel Tuner
• SWAR compression v2.2 5.7 +/- 4.6
• Material values (PeSTO)
• Piece square tables (PeSTO)
• Tapered Eval
• Tempo
• Mobility

UCI Functionality (adapted from gediminas' code)

Most basic UCI commands

• uci
• setoption name [name] value [value]
• position [startpos/FEN] [moves]
• isready
• go [wtime] [winc] [btime] [binc]

Options

• Hash type spin default 201 min 1 max 1024 - TT Hash size in MB
• rfpMargin type spin default 55 min 0 max 200 - Reverse Futility Pruning margin
• futilityMargin type spin default 116 min 0 max 400 - Futility Pruning margin
• hardBoundTimeRatio type spin default 10 min 1 max 100 - Hard Bound time management ratio
• softBoundTimeRatio type spin default 40 min 1 max 300 - Soft Bound time management ratio

Other nonstandard commands

• sevel - Get the static evaluation of the position

Log of feature addition

Log after v2.1
---------------
v2.2 - SWAR test for compressed eval for speedup
Score of SWARtest vs Original: 5383 - 5132 - 4808  [0.508] 15323
...      SWARtest playing White: 3347 - 1892 - 2423  [0.595] 7662
...      SWARtest playing Black: 2036 - 3240 - 2385  [0.421] 7661
...      White vs Black: 6587 - 3928 - 4808  [0.587] 15323
Elo difference: 5.7 +/- 4.6, LOS: 99.3 %, DrawRatio: 31.4 %
SPRT: llr 2.95 (100.3%), lbound -2.94, ubound 2.94 - H1 was accepted

v2.3  - Check for non pv before pruning or reducing in tt
(COMPUTER BLUESCREENED HALFWAY SO THIS IS JUST PARTIAL RESULTS)
Score of NoTTCutoffsInPv vs Original: 2204 - 2080 - 1824  [0.510] 6108
...      NoTTCutoffsInPv playing White: 1359 - 788 - 908  [0.593] 3055
...      NoTTCutoffsInPv playing Black: 845 - 1292 - 916  [0.427] 3053
...      White vs Black: 2651 - 1633 - 1824  [0.583] 6108
Elo difference: 7.1 +/- 7.3, LOS: 97.1 %, DrawRatio: 29.9 %
SPRT: llr 1.64 (55.8%), lbound -2.94, ubound 2.94

v2.4 - Budget aspiration window search
Score of ASP vs Original: 1307 - 1139 - 1072  [0.524] 3518
...      ASP playing White: 810 - 433 - 516  [0.607] 1759
...      ASP playing Black: 497 - 706 - 556  [0.441] 1759
...      White vs Black: 1516 - 930 - 1072  [0.583] 3518
Elo difference: 16.6 +/- 9.6, LOS: 100.0 %, DrawRatio: 30.5 %
SPRT: llr 2.96 (100.4%), lbound -2.94, ubound 2.94 - H1 was accepted

v2.5 - Delta pruning
Score of DeltaPrune vs Original: 2000 - 1817 - 1615  [0.517] 5432
...      DeltaPrune playing White: 1252 - 668 - 796  [0.608] 2716
...      DeltaPrune playing Black: 748 - 1149 - 819  [0.426] 2716
...      White vs Black: 2401 - 1416 - 1615  [0.591] 5432
Elo difference: 11.7 +/- 7.7, LOS: 99.8 %, DrawRatio: 29.7 %
SPRT: llr 2.95 (100.2%), lbound -2.94, ubound 2.94 - H1 was accepted

v2.6 - Correct ASP window search
Score of ASP vs Original: 3391 - 3179 - 2721  [0.511] 9291
...      ASP playing White: 2084 - 1259 - 1304  [0.589] 4647
...      ASP playing Black: 1307 - 1920 - 1417  [0.434] 4644
...      White vs Black: 4004 - 2566 - 2721  [0.577] 9291
Elo difference: 7.9 +/- 5.9, LOS: 99.6 %, DrawRatio: 29.3 %
SPRT: llr 2.95 (100.3%), lbound -2.94, ubound 2.94 - H1 was accepted

v2.7 - Tuned eval + changed mobility
(BLUESCREENED)
Around 7 elo

v2.8 - Speed up evaluation - extract only at the end
Score of SpeedUp vs Original: 902 - 733 - 544  [0.539] 2179
...      SpeedUp playing White: 538 - 284 - 268  [0.617] 1090
...      SpeedUp playing Black: 364 - 449 - 276  [0.461] 1089
...      White vs Black: 987 - 648 - 544  [0.578] 2179
Elo difference: 27.0 +/- 12.6, LOS: 100.0 %, DrawRatio: 25.0 %
SPRT: llr 2.95 (100.1%), lbound -2.94, ubound 2.94 - H1 was accepted

v2.9 - RFP changed to 55;
...      RFP55 playing White: 3188 - 1958 - 1745  [0.589] 6891
...      RFP55 playing Black: 2148 - 3124 - 1617  [0.429] 6889
...      White vs Black: 6312 - 4106 - 3362  [0.580] 13780
Elo difference: 6.4 +/- 5.0, LOS: 99.4 %, DrawRatio: 24.4 %
SPRT: llr 2.95 (100.1%), lbound -2.94, ubound 2.94 - H1 was accepted

v3.0 - New futility pruning
Score of NewFP vs Original: 1646 - 1461 - 1002  [0.523] 4109
...      NewFP playing White: 953 - 603 - 499  [0.585] 2055
...      NewFP playing Black: 693 - 858 - 503  [0.460] 2054
...      White vs Black: 1811 - 1296 - 1002  [0.563] 4109
Elo difference: 15.7 +/- 9.2, LOS: 100.0 %, DrawRatio: 24.4 %
SPRT: llr 2.96 (100.5%), lbound -2.94, ubound 2.94 - H1 was accepted

v3.1 - Retuned eval with mobility
Score of ReplacedEval vs Original: 1807 - 1610 - 789  [0.523] 4206
...      ReplacedEval playing White: 1026 - 674 - 404  [0.584] 2104
...      ReplacedEval playing Black: 781 - 936 - 385  [0.463] 2102
...      White vs Black: 1962 - 1455 - 789  [0.560] 4206
Elo difference: 16.3 +/- 9.5, LOS: 100.0 %, DrawRatio: 18.8 %
SPRT: llr 2.96 (100.4%), lbound -2.94, ubound 2.94 - H1 was accepted

Special thanks to (in no particular order)

• Sebastian Lague (For hosting the tiny chess bot tournament, although I couldn't submit on time)
• Ciekce (For helping with a lot of engine-related stuff)
• cj5716 (For helping with a lot of engine-related stuff)
• arandomnoob(on discord) (For helping with a lot of engine-related stuff)
• Toanth (For hosting the 400 token challenge to really get me into chess programming)
• Gediminas - for texel-tuner and stuff related to tuning
• jw (nnue stuff and bullet)
• and many other people in sebastian lague's chess programming server / the engine programming server

Engines I took inspiration from (in no particular order)

• Stormphrax
• Boychesser
• Smol.cs / NOSPRT
• 200 token monstrosity
• Atadofanoobbot
• Viridithas
• Ethereal
• Altair

Resources I found useful

• https://minuskelvin.net/chesswiki/ (Updated Chess programming wiki)
• https://www.chessprogramming.org/ (Old Wiki)
• https://github.com/cosmobobak/viridithas/blob/master/wiki.md (Small repository of search optims)
• https://discord.gg/S3MMh67q (Sebastian Lagues's chess programming serever)
• https://discord.gg/dVgkdqqt (Engine programming server)

TODO

Search

• Aspiration window v2.4 16.6 +/- 9.6
• Fail-Soft Negamax Search
• Quiescence Search
• Principle Variation Search
• Triple PVS v1.5 21.3 +/- 11.1
• Lazy SMP multithreading
• Pondering

Pruning

• Actual TT pruning v2.1 136.4 +/- 31.2
• A/B Pruning
• Null Move Pruning
• Reverse Futility Pruning
• Futility Pruning (depthdepthmargin) v3.0 15.7 +/- 9.2 vs Normal futility pruning
• Quiescence Search Standing Pat Pruning
• Quiescence Search Delta Pruning v2.5 11.7 +/- 7.7
• Mate distancing pruning
• Static Exchange Evaluation Pruning (QSearch)
• Late Move Pruning
• Multicut
• Prob-cut
• History leaf pruning
• Parity pruning
• Uncertainty cutoffs
• AEL-Pruning
• Enhanced forward pruning

Reductions

• Internal Iterative Reduction
• Late move reductions with triple pvs
• Internal Iterative deepening
• Fail-high reductions
• Rank-cut
• Razoring

Extensions

• Check Extensions
• Capture extensions
• Mate threat extensions
• One reply extension
• Passed pawn extension
• Pv extension
• Recapture extension
• Singular extensions

Ordering

• TT Moves
• MVV-LVA (for good captures)
• iller moves (quiets)
• History moves (quiets) v2.0 67.9 +/- 20.9
• History gravity
• History ageing
• History malus
• 1-ply continuation history
• 2-ply continuation history
• More extensive MVV-LVA ordering
• Capture history
• Counter-moves

Time Management

• Hard Bound
• Soft Bound

Evaluation

• Piece Square Tables
• Piece Weights
• Tempo
• Piece mobility (no king no pawn)

Pawn

• Pawn shield
• Pawn storm
• Strong pawn bonus
• Doubled pawn malus
• Passed pawn bonus
• Phalanx pawn bonus
• Isolated pawn malus

Piece

• Piece attacking enemy bonus
• Pawn defending piece bonus
• Trapped piece malus

General Major Pieces

• Major pieces on open file bonus
• Major piece on semi-open file bonus

General Minor Pieces

• Minor piece outpost bonus
• Undefended minor piece malus

Knight

• Pawn-count relative weight
• Blocking C-Pawn malus (in closed openings)
• Omit squares controlled by enemy pawns for mobility

Bishop

• Bishop pair
• Bad bishop
• Color weakness (also considering majority of pawns on what colored square)
• Fianchettoed bishop bonus (a fianchettoed bishop shouldn't be exchanged)
• Returning bishop bonus

Rook

• Pawn-count relative weight
• Rook behind passed-pawns
• Rook blocked by uncastled king malus
• Rook connecting bonus

Queen

• Early development malus

King

• King cornering for endgame checkmate (UNTUNED!!)
• King tropism
• King-relative PSQTs
• King Virtual mobility
• King on open file malus
• King on semi-open file malus
• King-relative to pawn chain malus
• Attacking king zone
• X-Rays/pins malus
• Castling rights