Monday, July 2, 2018

Season 12 superfinal, games 67-70

After 70 games Stockfish leads 18-7 with 45 draws. The draw rate continues to be low, now at 64.3%. Stockfish with two more wins, in the last 14 games the score is 6-0 for Stockfish.

In game 34.1 Stockfish pushed its central pawns and kept its king uncastled and exposed. Despite this its eval was over 1 and slowly increasing as the engines exchanged pieces. On move 27 only RRB vs RRN remained.

Stockfish's eval reached 2.5 and stayed there for a while as it was trying to find a way to break Komodo's defense. The engines played a long PV line that included trading the minor pieces, then on move 40 Stockfish's eval jumped over 3. What did it see?

Almost all the black pawns were isolated and difficult to protect. Komodo was close to zugzwang and it gave a pawn on the queen side. Stockfish had several easy targets, the white king moved to the queen side and a rook switched to the king side, causing Komodo to lose a second pawn.

Stockfish now had two passers on the queen side, it captured another pawn before the game was adjudicated.

In the reverse game 34.2 Komodo took the time to castle its king. The engines kept their pieces on the board much longer, the evals peaked around 0.6 and started to come down. After a series of exchanges the game reached a RBN vs RBN position. Komodo gave a bishop to create a passer on the queen side, Stockfish gave a rook to stop the passer. The game ended in a R vs B tablebase draw.

In game 35.1 Stockfish kept its king uncastled in the center. Komodo pushed pawns on the queen side and had a space advantage, Stockfish countered on the king side but evals turned negative and increasing. Komodo pushed the white pieces back and had strong central knights. The white king walked to the king side and the engines started to shuffle. Stockfish traded a bishop for one of the knights, allowing Komodo to get a passer on the 3rd rank, and shuffling resumed. On move 115 Komodo took a pawn to reset the 50-move counter, evals were over 2 and increasing. The position opened and most pieces were exchanged, leading to a QB vs QB position. Komodo took out white pawns and was 3 pawns up with evals over 4, Stockfish forced a queen exchange resulting in an opposite color bishop ending. Incredibly Stockfish was able to hold, the pawn structure and position of the kings did not allow Komodo to push its pawns forward. After another shuffle period Komodo moved a pawn, allowing Stockfish to take out 3 pawns for a bishop. The white king walked to the queen side corner and Komodo could not force it out. Stockfish pulled out an incredible draw, the longest game of the match so far at 238 moves.

In the reverse game 35.2 Komodo castled its king, Stockfish had a pawn majority on the queen side and Komodo had a central passer. Then Stockfish gave 3 pawns and captured a knight, giving Komodo a king side passer and opening the position.

The engines traded pawns and pieces. Stockfish lost its queen side pawns, and after exchanging a pair of rooks and the queens only R vs RN remained, Stockfish with one last pawn while Komodo had 4. Evals were negative over 1 with a long PV agreement that looked drawish. Then on move 55 Stockfish deviated from the line and its eval jumped over 6!!

A few moves later Komodo saw it was lost as well and the game was adjudicated. It was far from clear how Stockfish was going to win, its PV showed a line where the two white pawns were gone. Komodo however did not follow that line in its last move, and in its PV the pawns were still intact. An 8-man tablebase is needed to understand this fully.

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