Tuesday, December 1, 2015

Season 8 superfinal, games 71-80

After 80 games in the Komodo-Stockfish superfinal match, Komodo is leading 6-1 with 73 draws. In the last 10 games Komodo has struck twice, both wins in black, both started with white having an advantage. With only 20 games left is seems almost certain that Komodo will win the match. The two wins by Komodo also show that it is better than Stockfish in getting out of long shuffles with a winning position.

With two decisive games and several exciting draws, Cato's opening choices are doing well.

Game 71 started with a small eval advantage for Komodo, which then decreased gradually to 0 when there were only RRN vs RRN left. Stockfish had a passed pawn that wasn't going anywhere but may be the reason Stockfish gave a negative eval at this stage. There came a long period of shuffling that got close to the 50-move mark, and after a Komodo pawn move there came a gradual removal of all pieces. The game stopped at a drawn RN vs R tablebase position. Game 72 started similarly with a small eval advantage for Stockfish. Starting from move 20 the engines shuffled for 25 moves, while all pieces were still on the board.

Here Stockfish pushed the b pawn with Komodo countering with the f pawn, a few moves later the board was less crowded.

Stockfish's king looked a little vulnerable, and the evals favored Komodo - why stop shuffling if this is the result? Komodo put its knight on f3 making life harder for the white king and gradually increasing the eval. After queens were exchanged Komodo put a rook on the second rank and the pressure on the white king increased.

Could Stockfish hold this position? After a rook exchange Komodo used a threat on the h pawn and its passed e pawn to force Stockfish to lose the bishop for a pawn.

Stockfish was lost here, both engines saw that the white pawns were soon to be captured and the last black pawn couldn't be stopped. Stockfish lost the game just because it wouldn't continue the shuflling, and Komodo saw how it could turn the game around better than Stockfish. Well done Komodo, Stockfish needs to improve its skills.

Game 73 was a bit wild, with exposed kings and advancing passed pawns for both engines. Komodo started with an eval advantage, but as the game progressed and the threats became evident the evals went closer to 0, and then Komodo went for a RNP vs Q trade. What could have been an interesting imbalance turned into a perpetual check draw in a few moves. Game 74 started with a rook for bishop exchange by Komodo, followed by a queen exchange, but then the action stopped. By move 22 the game reached a RRB vs RBB endgame, and gradually the pawn structure made it difficult for the pieces to move and a draw was adjudicated.

In game 75 the evals went down to 0 in a quiet game, and then when the draw was sure the action started. A rook for bishop exchange, a rook and queen sacrifice followed by a queening and regaining the rook, and finally another  rook sacrifice and a perpetual check. A roller coaster draw. In game 76 Stockfish was able to keep an eval advantage of about 0.7 well into the game, reaching a RB vs RN endgame by move 30 with a pawn advantage. That's as far as it got for Stockfish, Komodo patiently exchanged pawns and the evals kept going down until they reached 0 again.

In game 77 all the queen side pawns were taken by move 21, and by move 31 the only pieces left were B vs N. The game continued until a tablebase draw, at least the game was relatively short.In game 78 most of the pawns remained on the board with the heavy pieces in a standoff behind them.

Stockfish started seeing repetitions in the PV while Komodo saw a small advantage in eval, two warning signs for Stockfish fans. Stockfish put all possible pressure on the c6 pawn, neglecting the king side.

Komodo very quickly took advantage, breaking the pawn structure on the king side and trapping the white king.

By the time Stockfish could untangle its pieces it was too late. It was an exchange down, the king trapped and with too many pawns to defend.

The game was adjudicated but the PV shows that once queens are exchanged there is nothing to stop the rook from attacking the pawns from behind, the bishop cannot defend them all and the king is too far away. So, another win for Komodo, again showing it gets out of pawn blockades better that Stockfish. Is Komodo just seeing farther than Stockfish? Is this the result of a bug?

Games 79 and 80 started with a pawn advantage for white out of the opening. In game 79 after many captures by move 24 all queen side pawns were gone except for a passed pawn for Komodo, and a few moves later the remaining pieces were BN vs BN with opposite colored bishops. Komodo kept an eval advantage for many more moves but could not advance the passed pawn or make any progress on the king side. After a few more exchanges the game was finally adjudicated on move 113. In game 80 Stockfish kept a pawn advantage on the queen side but quite unexpectedly gave a rook for a knight. The white pieces were much more active than the black pieces as compensation, and Stockfish managed to capture a second pawn. In the RN vs RR endgame Komodo blocked the white pawns advancing and finally gave the exchange back to get a pawn back. Material equality was reached after the remaining rooks were exchanged and though both sides queened a pawn no side had an advantage.

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