Tuesday, May 21, 2019

Season 15 superfinal, games 41-50

After 50 games Leela leads 8-5 with 37 draws. Stockfish won two minimatches and Leela's lead is down to 3 points. In both wins the game was heading for a draw and the change in evals came very late when Leela was short on time. 

There were no exchanges for the first 24 moves in game 41, Leela's eval came down and Stockfish's eval stayed around 1. The engines opened a file on the queen side, then Leela gave a pawn on the king side. Stockfish had a passer but all the white pawns were blocked. The engines shuffled for a while, Leela gave a second pawn but Stockfish couldn't break the black defense. After a series of exchanges Leela regained the material and the position opened. Stockfish ended the game with perpeteual check. In the reverse game 42 there were many early exchanges and only RBN vs RNN were left on move 24. Leela's eval was around 1.5 for a while, after some shuffling the engines reduced to a rook ending. Leela's eval came down and the game ended in a tablebase draw.

The black king moved early in game 43, it was exposed on the king side but Stockfish didn't try to attack. Leela was surprised by Stockfish's move 19 and its eval jumped over 2.5, in a long series of exchanges the engines reduced to a QB vs QB position with Stockfish a pawn up.

There were a few pawns moves and exchanges, and then a long shuffle. It appeared that the game was heading for a draw, evals remained constant or slowly decreasing. Leela was getting short on time and perhaps this caused the blunder, it let Stockfish exchange queens on move 79. Leela's eval jumped over 2.5, but Stockfish saw mate after a few moves.

Leela realized it was losing much too late. There was no way to prevent Stockfish from taking the a pawn, and Leela couldn't stop both white pawns.

In game 44 the black king side was open and Stockfish castled long. Leela's eval was around 2, queens were off early and there were several exchanges until move 23. The engines started to shuffle with pawn moves resetting the 50-move counter. On move 120 the engines exchanged a pair of rooks and only RBB vs RBN remained. The next exchange was on move 163, the engines slowly reduced to a B vs N ending. The network crashed on move 201, and since it was a drawn 7-man position the game was not resumed but manually adjudicated a draw.

There were a few exchanges early in game 45, but none from move 8. The engines formed pawn lines and stayed behind them, Leela pushed a pawn to a3, Stockfish pushed its king side pawns. Evals stayed under 1, from move 40 the pawn moves stopped and the engines started to shuffle. Stockfish's eval started to increased on move 77, Leela was short on time and its moves may have been less than perfect. On move 84 pawn moves ended the shuffle,  Stockfish had a passer in the center and a knight on g6, evals were over 3.

A series of exchanges opened the position, when it was over Stockfish was up two pawns with two advanced passers.

Leela tried to counter attack with its queen and rook through the queen side. This left the black king vulnerable, Stockfish protected its king and attacked the king side. The game was adjudicated with mate in the PV. 

In game 46 Leela moved its king without castling, it pushed its king side pawns and had a space advantage. There were no pawn exchanges until move 25, Leela's eval was over 3 when Stockfish gave a pawn and the engines opened two files on the queen side. The engines shuffled for a while, on move 52 the queens were exchanged and Leela's eval was over 4.5. All the pawns were blocked, Leela gave a rook for a bishop and two pawns to create a queen side passer in a RB vs RR position. Stockfish's eval dropped, it allowed Leela to capture a pawn and found a perpetual check draw.

Evals came down quickly in game 47 and they remained low throughout the game. The engines gradually exchanged pieces and the game reached a RB vs RN position on move 35. The game was soon adjudicated. In game 48 the black king side rook moved early and Stockfish kept its king uncastled. Leela's eval kept climbing, peaking over 2. The engines exchanged several pieces and played mostly behind the pawn lines. On move 39 the pawns stopped moving, Leela couldn't find a way to improve and its eval slowly came down. The game ended with the 50-move draw.

Evals were around 1 at the start of game 49. There were no pawn exchanges for the first 23 moves, then the engines exchanged pawns and opened the queen side. By move 34 all the pawns on the queen side were gone and evals came down. The game reached a RBN vs RBN position and ended in a tablebase draw. In game 50 again the engines waited before exchanging pawns. After a long series of exchanges that ended on move 29 Stockfish was a pawn up, there were open files on both sides of the board controlled by Leela's rooks. Stockfish's eval came down to 0 as the engines shuffled for almost 50 moves. The engines exchanged the remaining pieces and reached a rook ending. Both had passers, first Stockfish gave a rook queened and then Leela did the same. Leela's eval was over 2 but the queen ending was a draw, the game was adjudicated on move 158.

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