S14 bonus match, Leela - Stockfish, bookless openings

Leela beat Stockfish in a 100 rapid game match with no book, the end result was 16-4 with 80 draws. Leela learned a lot about openings in its training, and it appears to be better than Stockfish from the initial position, at least in shorter time controls. The match also shows that when the engines are allowed to choose the openings we get far less variety than what we usually see in TCEC.

In the 50 games Leela was white it always started with e4, Stockfish played either c5 (Sicilian) or e6 (French). Most of the Sicilians were a Najdorf, English attack variation, 30 games (60%) started with the same 15-ply opening. The French Defense games were mostly Steinitz Boleslavsky variations, 16 games (32%) had the same 13-ply opening. After 20 plys there were only 12 different sequences with information content ( = distribution entropy) equivalent to a space of size 6.4.

Stockfish played e4 in 76% of its white games, it started 24% with d4. Leela answered e4 with e5, leading to many Ruy-Lopez games and a few Italian games. 25 games (50%) started with an 16-ply Berlin Defense line, 11 games (22%) were Giuoco Pianissimo and more variable. Leela answered d4 with Nf6, and this led to QGD games, 7 games (14%) started with a 16-ply sequence in the Vienna variation. After 16 plys there were 19 different sequences with information content ( = distribution entropy) equivalent to a space of size 7.9.

Leela is more stubborn than Stockfish in its opening moves. All the major opening classes in the first few moves - Sicilian, French, Ruy Lopez, Italian, QGD - were determined by Stockfish either in black or in white. Stockfish expanded the opening tree almost every move in at least one opening line, again in both white and black. Leela, on the other hand, almost always played the same move when presented with the same position. In the first 24 plys of 100 games I found only 3 cases where Leela expanded the opening tree, on move 7 as black in QGD (game 29), on move 10 as black in Ruy Lopez (games 45 vs 97), and on move 10 as white in French (game 84).

As white Leela won 6/30 in the Sicilian Najdorf, and lost 2/30. In the French Defense Leela won 5/17 games and lost none. As black in the Italian games Leela won 4/11 and lost 1/11, not a good choice for Stockfish. In the Ruy Lopez Leela won 1/27, the rest were draws. Stockfish won 1/8 in the QGD.