Wednesday, October 7, 2020

Season 19 superfinal games 21-30

After 30 games the score is tied 3-3 with 24 draws. Leela won its first game pair. There was a long shuffle in the game it won, the engines were in blitz mode after that. Perhaps this is a good strategy against Stockfish? There were two openings with a 2-ply book and in both pairs the games repeated for more than 11 moves. It seems Stockfish NNUE plays openings like Leela.

Games 21-22 started with a 2-ply book 1.e4 e5. Game 21 followed a high level line in the Ruy Lopez Berlin defense opening. Evals were low throughout the game, almost all pawns stayed on the board except a file that was opened in the center. The engines gradually exchanged pieces, on move 31 the game reached a same color bishop ending. The draw rule stopped the game 35 moves later. Game 22 followed the same line until move 12 (does Stockfish NNUE have the same opening rigidity that Leela has shown in the past?), evals again were low throughout the game. Queens were off early and the game reached a RBB vs RBN position on move 26, the engines started to shuffle and the game was adjudicated quickly.

The book exit in games 23-24 had black a pawn up, white threatening to take a rook on the long diagonal, and the white king unable to castle after it moved. In game 23 the engines played out a long PV agreement and Leela captured the rook for a bishop. Stockfish could not castle its king and both king side rooks were trapped. Evals gradually increased as the engines exchanged pieces, the game reached a RRN vs RBN position on move 33. Both kings left the back row to open a path for the trapped rooks, Stockfish had a pawn majority on the queen side and it created a passer.

The engines started to shuffle, it was reasonable that Leela would try something with its king side pawns but it seemed reluctant to do this. A few times in its PV Leela suggested Stockfish move a pawn, Stockfish kept shuffling and Leela's eval slowly came down. After 25 moves Leela pushed e4, but its eval continued to drift downwards. Leela moved its king forward and on move 77 it played e5. Quite unexpectedly Stockfish's eval jumped over 3.5 while Leela's eval did not change at all. The position opened and the knights were exchanged, it took Leela a few moves to start increasing its eval. The white rooks had open files and Leela captured a pawn. Stockfish's eval showed it was certain the game was lost.

Leela moved its rooks forward, the black rook was too far away and could not get back and Leela captured the bishop for the win.

In game 24 Stockfish immediately regained the pawn but it would not take the black rook. Leela had time to castle its king and move the rook to safety. Stockfish's eval was above 0.5 for a while, but it came down after the engines reduced to a RRN vs RRN position on move 28. Stockfish managed to capture a pawn but no more, the engines started to repeat and shuffle and the game was adjudicated. Leela wins its first game pair and the score is tied again.

Games 25-26 started with a 2-ply book 1. e4 d5. The engines followed a high level line in the Scandinavian defense for 13 moves with evals around 0.5. Stockfish castled short despite a white pawn on h6, its eval came down when its queen came forward and threatened the exposed white king. Stockfish got rid of the h6 pawn and Leela's eval came down as well. The engines exchanged pieces and the draw rule was applied in a QB vs QB position. Game 26 diverged on move 14, a long agreement like in games 21-22. Again Leela castled short and Stockfish had a pawn on h6. Almost all pawns stayed on the board, Leela stayed back and fortified a defense line. The engines started to shuffle on move 26, evals came down and the game was quickly adjudicated.

Games 27-28 started with white a pawn up in a Blumenfeld counter gambit. In game 27 Stockfish gave the pawn back, it had strong central pawns with one passer. The black king was exposed in the center, Leela captured a pawn while the black king walked to the queen side. Stockfish's eval dropped to 0, Leela prepared to attack and captured another pawn. However, Leela's eval also dropped and Stockfish forced a repetition draw. In game 28 Stockfish kept the pawn and both engines castled. After a series of exchanges all the queen side pawns were gone, Leela regained the pawn and it had an advanced passer in the center. Evals were close to 0, the engines reduced to a QR vs QR position, Stockfish captured the passer and the game was adjudicated.

Stockfish pushed pawns on the queen side in game 29, Leela kept its king uncastled. The game reached a RRN vs RRN position on move 23, evals came down as the exchanges continued. The engines reduced to a double rook ending, the game was adjudicated when the pawns stopped moving. In game 30 Stockfish placed its queen on h6 and castled long. Leela had to protect its king and could spare only a few resources for a queen side attack. Evals dropped to 0, the engines were close to a repetition draw but reduced to a drawn rook ending instead. The game ended 14 moves later.


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