1. History

2. Program & Use

3. Competition results
    Results summary 

4. Notable games

5. See also

6. References

7. External links

Leela Chess Zero is a free, open-source, and neural network based chess engine and distributed computing project. Development has been spearheaded by programmer Gary Linscott, who is also a developer for the Stockfish chess engine. Leela Chess Zero was adapted from the Leela Zero Go engine,^[1] which in turn was based on Google's AlphaGo Zero project,^[2] also to verify the methods in the AlphaZero paper as applied to the game of chess.

Like Leela Zero and AlphaGo Zero, Leela Chess Zero only knows the basic rules and nothing more.^[1] Leela Chess Zero is trained by a distributed computing network coordinated at the Leela Chess Zero website. As of March 20 2019, Leela Chess Zero has gained an self-play Elo rating of 3,125 from playing 192,841,908 games of chess.^[3]

History

The Leela Chess Zero project was first announced on TalkChess.com on January 9, 2018.^[1][4] This revealed Leela Chess Zero as the open-source, self learning chess engine it would come to be known as, with a goal of creating a strong chess engine.^[5] Within the first few months of training, Leela Chess Zero had already reached the Grandmaster level, surpassing the strength of early releases of Rybka, Stockfish, and Komodo, despite evaluating orders of magnitude fewer positions while using MCTS.

In December 2018, the AlphaZero team published a new paper in Science magazine revealing previously undisclosed details of the architecture and training parameters used for AlphaZero.^[6] These changes were soon incorporated into Leela Chess Zero and increased both its strength and training efficiency.^[7]

Program & Use

The basis of which Leela Chess Zero has used to self-learn, and play chess at a super human level is with Reinforcement learning. This is a machine learning algorithm, mirrored from AlphaZero to be used by Leela Chess Zero, to maximize reward to make the engine a better chess player through self-play.^{[6] [1]}From open-source, Leela Chess Zero has played hundreds of millions of games, run by volunteer users, in order to learn with the reinforcement algorithm.^[3] In order to contribute to the advancement of the Leela Chess Zero engine, the latest version of the Engine as well as the Client must be downloaded. The Client is needed to connect to the current server of Leela Chess Zero, which all of the information from the self-play chess games are stored, to obtain the latest network, generate self-play games, and upload the training data back to the server.^[8]

If, however, someone would like themselves to play against Leela Chess Zero engine, the Network must be downloaded. The Network contains Leela Chess Zero's evaluation function that is needed for the opponent to play against the engine.^[8] Playing against a past form of the Leela Chess Zero engine is also possible. Although, the self-play rating calculated for the engine is different from the conventional Elo chess rating. In order to find the self-play rating of Leela Chess Zero from Elo rating is to use the formula:

X = (y + 511.7)/0.6

Where y is the players Elo chess rating, and X is Leela Chess Zero's self-play rating.^[9]

Competition results

In April 2018, Leela Chess Zero became the first neural network engine to enter the Top Chess Engine Championship (TCEC), during season 12 in the lowest division, division 4.^[10] Leela did not perform well: in 28 games, it won one, drew two, and lost the remainder; its sole victory came from a position in which its opponent, Scorpio 2.82, crashed.^[11] However, it improved quickly. In July 2018, Leela placed seventh out of eight competitors at the 2018 World Computer Chess Championship,^[12] and in the next TCEC season, it won division 4 with a record of 14 wins, 12 draws, and 2 losses.^[13] After being promoted to division 3, Leela tied for 2nd place with Arasan, but did not advance. (In the event of a tie, direct encounters between the tied engines decide promotion.) Its record in division 3 was 7 wins, 18 draws, and 3 losses.^[13]

In August 2018, Leela Chess Zero had taken first place in the season 13 Top Chess Engine Championship (TCEC), division 4. Leela was 1.5 points ahead of the second place engine, Deus X, powered by the Leela Chess Zero engine, with 20/28 points. Leela had made it into the division three championship to face even stronger opponents with Elo ratings greater than Leela's, along with Dues X with 18/28 points. At first, the Leela Chess Zero engine was winning many games in the early rounds with only a few draws. By round 7, Leela was facing off against the top conventional chess engine in division 4, Wasp, unfortunately losing the round. Further rounds had Leela needing to gain every point in order to win the Championship and had only gained secure qualification in the final rounds against the other engines. In the end, Leela Chess Zero had 14 wins, 12 draws, and 2 losses.^[14] Leela Chess Zero then went on the get 16/28 points in division 3 of the TCEC, losing to Ethereal, with 22.5/28 points, and a direct tiebreak match against Arasan, obtaining third place.^[15]

By September 2018, Leela had become competitive with the strongest engines in the world. In the 2018 Chess.com Computer Chess Championship (CCCC),^[16] Leela placed fifth out of 24 entrants. The top eight engines advanced to round 2, where Leela placed fourth.^[17][18] Leela then won the 30 game match against Komodo to secure 3rd place in the tournament.^[19][20] Concurrently, Leela participated in the TCEC cup, a new event in which engines from different TCEC divisions can play matches against one another. Leela defeated higher-division engines Laser, Ethereal and Fire before finally being eliminated by Stockfish in the semi-finals.^[21]

In October and November 2018, Leela participated in the Chess.com Computer Chess Championship Blitz Battle.^[22] Leela finished third behind Stockfish and Komodo.^[23]

In December 2018, Leela participated in season 14 of the Top Chess Engine Championship. Leela dominated divisions 3, 2, and 1, easily finishing first in all of them. In the premier division, Stockfish dominated while Houdini, Komodo and Leela competed for second place. It came down to a final-round game where Leela needed to hold Stockfish to a draw with black to finish second ahead of Komodo. This it successfully managed, and therefore contested the superfinal against Stockfish. It narrowly lost the superfinal against Stockfish with a 49.5-50.5 final score.^[24]

In February 2019, Leela scored its first major tournament win when it defeated Houdini in the final of the second TCEC cup. Leela did not lose a game the entire tournament.^[25][26]

Results summary

Notable games

• [https://www.chess.com/news/view/stockfish-wins-computer-chess-championship-rapid-lc0-finishes-3rd-3887 Leela vs Stockfish, CCCC bonus games, 1-0] Leela beats the world champion Stockfish engine despite a 1-pawn handicap.

• In a game between Leela Chess Zero versus Chiron^[33], Leela had played over one hundred perfect moves against Chiron. With the shortest possible mate in 20 moves, the Leela engine decided to go against this outcome. Instead, Leela Chess Zero sacrificed her queen twice, gave up a rook and a knight, and promoted a pawn to less than a queen. Some thought this to be derision, and questioned whether Leela Chess Zero was mocking her opponent, since this type of behavior was so uncommon.^[34] Although, some believe this to have been a way for the Leela engine to safely execute check against Chiron, without causing accidental stalemates by clearing the material from the board, to make the game simpler, eliminating any problems that could appear for Leela.^[35]

See also

• AlphaZero

References

External links

• {{Official|http://lczero.org/}}
• [https://github.com/LeelaChessZero/lc0 Leela Chess Zero] on GitHub
• [https://github.com/LeelaChessZero/lczero-client/releases Neural network training client]
• [https://github.com/LeelaChessZero/lc0/releases Engine]
• [https://www.chessprogramming.org/Leela_Chess_Zero Chessprogramming wiki on Leela Chess Zero]

• Three Songs (EP)
• Three Songs (Ireland)
• Three Songs to poems by Arthur Symons
• Three (S.O.S. Band album)
• Three (Soulfly album)
• Three South
• Three Sparrows and a Bit
• Three spheres inequality
• Three spikelets
• Threespine grubfish
• Three-spool engine
• Three spot crimson tip
• Three Spot Crimson Tip
• Three-spot damsel
• Three-spot grass yellow
• Three spot skipper
• Three Spot Skipper
• Threespot squirrelfish
• Three-spotted crambus moth
• Three-spotted flea beetle
• Three-spotted nola
• Three-spotted pleasing fungus beetle
• Three-spotted skipper
• Three-spotted specter
• Three-square