Sunday, April 15, 2018

Season 11 superfinal, games 81-90

After 90 games Stockfish leads 18-2 with 70 draws. It is now official: Stockfish is the winner of the superfinal of season 11. Houdini can not close the gap in the remaining ten games.

Stockfish had an eval close to 1 at the start of game 81. It gave a pawn and opened the king side, took over the long diagonal looking at the black king and threatened mate on the h file. Stockfish's eval was over 2 very quickly.

Houdini exchanged pieces to get its king out of immediate danger. It was still a pawn up and had passers on both the king and the queen side, while Stockfish had a bishop pair, a central passer, and the black king was still exposed. Stockfish's eval was already above 3.

After exchanging a few pawns Stockfish put a rook on the 7th rank, and together with the bishop pair they confined Houdini's king and two pieces to the back rank.

The black pawns could not be defended and Stockfish created a second passer on the king side. With the two passers advancing the game was soon over. Houdini forced the black king to move without castling in game 82. Houdini's eval was around 0.8 for a while, but it came down as the engines opened files and exchanged pieces. The game reached a RB vs RB position and ended in a tablebase draw.

The engines castled in opposite directions in game 83. Stockfish pushed a pawn on the king side, weakening the black king position. Houdini pushed pawns on the queen side, Stockfish gave a rook for a bishop to eliminate one pawn. Stockfish captured another pawn in the center, creating a queen side passer, evals started to increase. Stockfish's eval peaked around 1.5, it had 4 queen side passers in a QBN vs QRB position. Houdini's pieces were very active and could attack the white king, Houdini gave back the material and got rid of two of the passers. Evals dropped to 0, it took the engines another 30 moves to reach a tablebase draw. In game 84 the engines again castled in opposite directions and pushed pawns in a similar manner. The files remained closed on both sides of the board, and after a few exchanges the engines started to shuffle on move 27. Evals came down to 0 and 55 moves later the engines opened the queen side and the game ended in a perpetual check draw.

Evals were close to 0 throughout game 85. The engines exchanged pieces gradually until reaching a rook ending. Stockfish lost its rook to stop a black pawn queening. Then Stockfish promoted a pawn, and Houdini was forced to close the game with perpetual check. There were many early exchanges in game 86, and only QRR vs QRR remained on move 21. The engines shuffled for a while and then reduced to a drawn rook endgame.

Houdini was a pawn up in game 87 with a queen side passer. Stockfish was ahead in development and it quickly equalized. Evals were close to 0 as Stockfish concentrated forces against the weak black king side and opened it by pushing pawns. Stockfish let Houdini capture a bishop on the queen side for a dangerous attack on the black king, which was strong enough to force a perpetual check draw. In game 88 Stockfish pushed the queen side pawns forward, ignoring the lack of development on the king side and keeping the king in the center. Houdini placed its rooks on the queen side and prevented the black passer from advancing. Evals dropped to 0 after a series of exchanges, Houdini eliminated the black passer and only RN vs RN remained. The game continued until reaching a tablebase draw.

Stockfish started game 89 with an eval advantage that increased gradually and was over 1 on move 20. Houdini had a pawn advantage on the queen side and it pushed its pawns forward. After a series of exchanges Stockfish won a pawn and QRB vs QRN remained. On move 44 after 12 minutes of thought Stockfish's eval jumped to almost 3. Houdini thought for 10 minutes and its eval also jumped. Both engines did not provide a PV that showed what they planned, however in the following move the evals dropped back, very strange. The engines traded pieces and the game reached a drawn B vs N ending.  Houdini had an eval advantage in game 90, an early series of exchanges left QRB vs QRN on move 22. Stockfish was up a pawn but its king was vulnerable. After exchanging queens the evals came down, the game reached a tablebase draw.

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