Friday, May 17, 2019

Season 15 superfinal, games 21-30

After 30 games Leela leads 5-1 with 24 draws. Leela gets two more wins, so far the only way Leela loses is by blundering in an endgame. We have not seen a weak opening for Leela until now.

Stockfish had a small eval advantage from the start of game 21. The engines opened the king side and Leela was able to get a pawn to f3, its eval turned slightly negative. The white king walked to the center, Leela shifted to the queen side and opened a file. Stockfish attacked the back rank with a rook, after a series of exchanges only RR vs RB remained. Leela was two pawns up with a queen side passer, Stockfish closed the game with perpetual check. In game 22 Stockfish's eval was 0 from the start and remained almost constant the entire game. There were only a few exchanges after the start, the engines developed behind pawn lines. A series of exchanges that started on move 28 opened the position, both engines had passers on the queen side. Leela pushed a passer to a6 and there it was blocked. After a while the engines reduced to a QRN vs QRB position and captured all the queen side pawns. Leela continued to play and the game ended in a tablebase draw on move 97.

Games 23-24 started with a 24-ply book in a closed Ruy Lopez. In game 23 evals started around 1 and slowly came down. Stockfish was strong in the center and Leela pushed pawns on the queen side. A series of exchanges cleared most of the pawns on the queen side by move 34, by move 47 only QRN vs QRB remained. Stockfish went a pawn up and reduced to a rook ending, 3 vs 2 pawns on the king side. It took almost 50 moves for Stockfish to lower its eval for the draw rule.

In game 24 Leela's eval started at 1 and slowly increased. There were almost no exchanges until move 28, Stockfish's eval stayed under 1. A series of exchanges opened the position, material was equal yet Leela's eval was over 2, Stockfish was still not convinced.

The engines exchanged a few pawns and evals continued to increase. The game reached a BN vs BN position on move 53 and Leela went a pawn up for the first time after taking the h4 pawn. Stockfish had connected passers in the center but Leela's passers on the two flanks were more dangerous. 

The kings went to the king side and the pieces to the queen side. Stockfish was too busy defending that it could not push its passers. Leela exchanged bishops and captured another pawn, the resulting knight ending was a win for white.

Games 25-26 started with a 21-ply book in the Queen's Indian defense, Fianchetto variation. In game 25 the engines opened the queen side early and Leela was up a pawn. Evals slowly came down, the engines mainly shuffled for a while. On move 30 the exchanges resumed and Stockfish equalized material. On move 43 the game reached a QBN vs QBN position and the game was adjudicated a few moves later.

The network crashed in game 26 and it was later resumed. It started identically to the reverse game up to move 17. Stockfish was a pawn up and had a queen side passer, Leela had the bishop pair advantage and more space. The engines started to shuffle on move 20 with a few pawn moves in between. On move 38 Leela gave a second pawn, and this led to a series of exchanges and a QRB vs QNN position.

For a while evals did not change. The engines exchanged pawns and queens, all remaining pawns were on the king side except for one isolated black pawn on the king side. The black knights were too far away and busy defending their king. Leela captured the a pawn, its eval jumping over 6.5.

The white pieces were stronger than the black knights. The game was adjudicated after Leela moved its king forward.

There were many early exchanges in game 27, by move 21 only RRB vs RRN remained. Stockfish was up a pawn while Leela pushed a pawn to h3 and had a rook on the 2nd rank. Stockfish captured a second pawn but evals were close to 0, the white king was in danger and Leela's control of the 2nd rank compensated for the material. The engines reduced to a rook ending and continued to play, the game ended in a tablebase draw on move 87. In game 28 both engines captured a rook in the corner early. The white king had to move but Leela's eval was over 1.5 and increasing. The white king walked to the queen side, Leela's eval peaked over 4 and the game reached a QRB vs QRN position on move 32. Stockfish gave a pawn and created an advanced passer, its eval dropped to 0 while Leela's eval remained around 3. Leela could not improve its position, it won a second pawn but eventually lowered its eval as Stockfish found a perpetual check draw.

In game 29 the engines opened the queen side early, both kings castled short and were not involved in the game. Evals started around 1 but came down as the engines fought for control of the open files. The rooks were first to go, then the queens and the game reached a drawn BBN vs BBN position. The network crashed again in game 30 and the game was later resumed. Stockfish's eval was close to 0 throughout the game. There were many early exchanges that opened the position and led to a R vs BB imbalance. Leela was two pawns up and it thought it had an advantage, Stockfish held the position without a problem. The game reached a R vs BB ending on move 45, Leela kept playing untile reaching a tablebase draw on move 166.

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