Ethereal

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Ethereal, an UCI compliant open source chess engine written by Andrew Grant in C, licensed under the GNU GPL and first officially released in June 2016. Ethereal is greatly influenced from Crafty, Stockfish, TSCP, MadChess, and Fruit. On October 09, 2020, Andrew Grant announced his withdrawal from Ethereal's development with his final releases of Ethereal V12.75 and Ethereal 12.75 SF-NNUE, the latter a NNUE implementation based on Stockfish NNUE, to deliberately demonstrate how everybody may considerably improve the playing strength of their engines without much effort - causing the author's frustration.

=Features=

Board Representation

 * Bitboards
 * Fancy Magic Bitboards
 * 8x8 Board

Search

 * Lazy SMP since 8.60 SMP
 * Iterative Deepening
 * Aspiration Windows
 * PVS Alpha-Beta
 * Transposition Table
 * Selectivity
 * Check Extensions
 * Delta Pruning
 * Futility Pruning
 * Late Move Reductions
 * Null Move Pruning
 * Razoring
 * Reverse Futility Pruning (Static Null Move Pruning)
 * Static Exchange Evaluation Pruning
 * Multi-Cut (12.00)
 * Move Ordering
 * Internal Iterative Deepening
 * MVV/LVA
 * Killer Heuristic
 * History Heuristic
 * Piece-Square Tables

Evaluation

 * NNUE (Ethereal 12.75 SF-NNUE)
 * Tapered Eval
 * Material
 * Piece-Square Tables
 * Mobility
 * Outposts
 * Rook on (Half) Open File
 * Rook on 7th Rank
 * Castling Ability
 * Pawn Hash Table
 * Pawn Structure
 * Automated Tuning by Logistic Regression, AdaGrad (12.50)

Misc

 * Syzygy Bases using Fathom's probing code (9.65), superseded by 7-men Pyrrhic (12.50)

=Publications=
 * Andrew Grant (2020). Evaluation & Tuning in Chess Engines.

=Forum Posts=

2016 ...

 * Re: How to speed up my engine by Günther Simon, CCC, May 03, 2016
 * Re: How to speed up my engine by Andrew Grant, CCC, May 03, 2016

2017 2018 2019
 * Ethereal Bitboard 6.26 Chess Engine...a star is born! by AA Ross, CCC, May 14, 2016
 * Ethereal - Official Release by Andrew Grant, CCC, June 25, 2016
 * Ethereal - Official Release by Andrew Grant, CCRL Discussion Board, June 25, 2016
 * Release of Ethereal7.78 by Andrew Grant, CCC, September 04, 2016
 * Official release of Ethereal8.16 by Andrew Grant, CCC, June 03, 2017
 * Ethereal8.28 Release by Andrew Grant, CCC, September 13, 2017
 * Ethereal8.37 Release by Andrew Grant, CCC, November 10, 2017
 * Release of Ethereal 8.60 SMP by Andrew Grant, CCC, December 10, 2017
 * Ethereal 8.61 -- Small bugfix to 8.60 by Andrew Grant, CCC, December 12, 2017
 * Time Managment translating to SMP by Andrew Grant, CCC, December 23, 2017 » Parallel Search, Time Management
 * Official Release of Ethereal9.00 by Andrew Grant, CCC, February 15, 2018
 * Official Release of Ethereal9.30 by Andrew Grant, CCC, March 20, 2018
 * Official Release of Ethereal9.65 with Syzygy Support by Andrew Grant, CCC, April 29, 2018
 * Official Release of Ethereal 10.00 (Two-years Anniversary) by Andrew Grant, CCC, May 30, 2018
 * Official Release of Ethereal 10.55 by Andrew Grant, CCC, July 16, 2018
 * Ethereal 10.88 NUMA by Norman Schmidt, CCC, August 24, 2018 » NUMA
 * Official Release of Ethereal 11.25 by Andrew Grant, CCC, January 21, 2019
 * For those that like to toy with Ethereal... by Dann Corbit, CCC, October 30, 2019
 * Official Release of Ethereal 11.75, supporting MultiPV by Andrew Grant, CCC, November 11, 2019

2020 ...

 * Official Release of Ethereal 12.00 by Andrew Grant, CCC, February 29, 2020
 * Pawn structure tuning by Vivien Clauzon, CCC, April 11, 2020 » Pawn Structure, Automated Tuning
 * Pyrrhic, Fathom for Humanoids by Andrew Grant, CCC, August 16, 2020 » Pyrrhic
 * Evaluation & Tuning in Chess Engines by Andrew Grant, CCC, August 24, 2020 » Automated Tuning
 * Official Release of Ethereal 12.50 by Andrew Grant, CCC, September 08, 2020
 * Ethereal Pawn-King NN by Andrew Grant, CCC, September 19, 2020
 * Final Release of Ethereal, V12.75 by Andrew Grant, CCC, October 09, 2020
 * Re: Final Release of Ethereal, V12.75 by Andrew Grant, CCC, October 09, 2020
 * Re: Final Release of Ethereal, V12.75 by Andrew Grant, CCC, November 12, 2020


 * Request for someone to train an NNUE for Ethereal by Andrew Grant, CCC, October 09, 2020 » NNUE
 * Ethereal Tuning - Data Dump by Andrew Grant, CCC, October 10, 2020
 * Ethereal questions by Gabor Szots, CCC, December 12, 2020

=External Links=

Chess Engine

 * GitHub - AndyGrant/Ethereal: Ethereal UCI Chess Engine
 * Ethereal in CCRL 40/4
 * Ethereal wins TCEC Division 4, Interview with Andrew Grant, Chessdom, April 30, 2018 » TCEC Season 12
 * Ethereal chess engine leads TCEC Div 3 convincingly, Chessdom, August 12, 2018 » TCEC Season 13
 * Ethereal chess engine wins the gold at TCEC Div 3, Chessdom, August 17, 2018

Misc

 * ethereal - Wiktionary
 * Ethereal from Wikipedia
 * Ether from Wikipedia
 * Ethereal wave from Wikipedia
 * Ethereal cardinal from Wikipedia
 * The Ethereal from Truth is Beauty, July 07, 2015
 * Jean-Luc Ponty - Ethereal Mood (1978), YouTube Video

=References= Up one Level