In the 15th Superfinal of the Top Chess Engine Championship (TCEC) – the unofficial computer chess World Championship – the self-learning Leela Chess Zero beat the previous best engine in the world, Stockfish 10. In a 100-game match (two hours per player, with a 10-second increment) Leela emerged victorious 53.5:46.5 (+14 =79 -7). In the qualification for the final it was still Stockfish 10 that had the edge, but in the final Leela was for the first time crowned the undisputed champion! Has this opened up a new age in computer chess?

What is the TCEC?
For years now the Top Chess Engine Championship has seen competition between the world’s best chess engines. It’s a league system with promotion and relegation, where engines that are improving gradually get to start in higher divisions. The higher the league, the longer the thinking time.
In the top league, the Premier Division, the eight best engines first play each other six times. After a total of 42 rounds the league is over – but not yet the season! The two chess engines that finished 1st and 2nd play each other in a clash of the titans – a duel fought out over no less than 100 games.

The career of Stockfish
This chess engine developed by Tord Romstad and others is probably known to almost all chess players. Its first version was developed in 2008 on the basis of the program Glaurung – an engine that Romstad had also developed in 2004. The dominance of Stockfish in recent years can clearly be seen from its placements and results in the TCEC:
Season 9 Superfinal: Stockfish 54.5:45.5 Houdini
Season 10 Superfinal: Stockfish missed out on the final after finishing unbeaten on 18/28 in the Premier Division, half a point behind Houdini and Komodo. Houdini won the final 53:47
Season 11 Superfinal: Stockfish (3546) 59:41 Houdini (3489)
Season 12 Superfinal: Stockfish (3519) 60:40 Komodo (3475)
Season 13 Superfinal: Stockfish (3519) 55:45 Komodo (3475)
Season 14 Superfinal: Stockfish (3588) 50.5:49.5 Leela Chess Zero (3404)

One thing is therefore clear: in recent years there was basically no getting around the Norwegian fish! Just as in human chess, Norway was alone at the top. In Superfinals 11-13 Komodo and Houdini didn’t have the slightest chance and the matches were soon over as contests. It was only in the last season that Stockfish came up against an equal, an opponent it could only beat by the narrowest of margins: Leela Chess Zero.

eela Chess Zero would never have appeared in its current form without the much-hyped competition between AlphaZero and Stockfish 8. AlphaZero, the algorithm developed by Google’s DeepMind, came from nowhere with the announcement that it had beaten Stockfish 64:36, with 28 wins to its opponent’s 0. It was hard to avoid seeing it as a revolution. Without any chess knowledge except the rules of the game, it took AlphaZero four hours of playing against itself to be able to beat the best engine in the world. Even if at the beginning there was loud criticism (critics said Stockfish had been given unfair conditions), there was no denying the reality. A second, more rigorous 1000-game match ended with AlphaZero winning 574.5:425.5, and further tests showed clear domination. …

Will that mark the end of conventional engines being able to compete in the TCEC and the start of a battle between competing self-learning neural algorithms? Or can Stockfish mount a comeback? These are interesting times for computer chess!

See also:

• DeepMind’s AlphaZero crushes chess
• AlphaZero really is that good
• Jan Gustafsson: Learn from AlphaZero & beat the Queen’s Indian

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