Friday, November 20, 2015

Season 8 superfinal, games 31-40

After 40 games in the Komodo-Stockfish superfinal Komodo leads by 3 wins to 1, with 36 draws. Stockfish has finally won a game, showing that it is possible to beat Komodo, just very very hard. On the other hand Komodo added another win too, this time playing black. My feeling - Komodo is going to win this match.

Game 31 started with both queens moving forward unsupported, followed by a queen exchange as well as many other pieces captured. The game reached a double rook endgame on move 25, with equal material and where Komodo had an isolated passed pawn. Stockfish had no problem defending until all pawns were gone but one that couldn't advance, another draw. Game 32 was only a little different, reaching a RN vs RN endgame on move 26. All pieces were eventually captured, the game ended in a drawn king and pawns position.

In game 33 Komodo had a small eval advantage that didn't get anywhere. Once all the heavy pieces were exchanged Komodo's knights were a little more effective than Stockfish's bishops, but it still ended a draw. In game 34 there were no castlings and the pawns blocked all files except one. Stockfish had more room and an eval advantage but there was no way to improve. Instead both engines shuffled a lot with one capture to avoid the 50 move draw once. The game was adjudicated before the 50 moves were reached the second time.

In game 35 Komodo's king became very exposed but Stockfish had a 0 eval. Komodo was able to stabilize its position, and after rooks were exchanged the white king was much safer and the game drifted into a draw. Game 36 took a different path, Stockfish held to a small eval advantage and the heavy pieces remained on the board. At move 37 the position was:

Here Komodo decided to sacrifice a pawn, perhaps to gain initiative or to get rid of the white bishop pair that was gaining strength. A few moves later all the light pieces were gone and Komodo had to defend carefully to keep the b pawn from falling as well.

The eval started to increase gradually, but with all the heavy pieces playing it seemed that Komodo had enough to defend as well as threat the white king. The engines maneuvered for a long time until the queens were exchanged.

Now Stockfish's plan was getting clear, exchange pawns and keep the rooks. Indeed this is what happened, with Stockfish holding on to the connected e+f pawns.

This was a decisive advantage that the engines could not ignore, and even the most skeptic of fans had to realize that Stockfish was really winning. Finally, a sigh of relief. Stockfish with a clear win, without a lot of help from the opening. A score of 2-1 is very close and there are still many games to be played. This was a happy Stockfish moment.

Game 37 was very quiet, nothing special from either side and evals close to zero throughout the game. A draw adjudication was reached at the first possible opportunity. Game 38 started in a similar way, but around move 20 Komodo took the initiative and the evals became slightly negative. At move 30 Komodo had more space but the position looked blocked and the PV showed only shuffling.

After 20 shuffling moves Komodo broke the pawn structure with f6 and the board cleared up a little. Stockfish was getting low on time, and after the queens were exchanged Komodo's eval increased a little, what was it planning?

The black b pawn and the white c pawn were eliminated with a bishop exchange as well, and Stockfish (and its fans) started to feel the pressure. Komodo's plan was still not clear and material was equal but something was happening.

 Komodo placed the knight on f5, effectively defending its pawns while attacking the white h pawn. Meanwhile the black rook could attack pawns, the bishop or the king. Eventually Stockfish lost the d pawn, creating dangerous black pawns in the center.

As they started marching together Stockfish had no choice but to sacrifice the bishop to stop them, and the evals jumped accordingly.

The 8-piece ending was still very difficult and the game was adjudicated long before the mate was in sight. Komodo had to hang on to its remaining pawn to avoid a theoretical draw, but both engines agreed that the end result would be a Komodo win. Back to 3-1, so close to Stockfish's first victory Komodo produces a win in black. And the reverse game was so boring, where did this come from?

Games 39 and 40 were two relatively short uneventful draws. In both games the two engines had their kings exposed to attack, and when a threat became serious enough the other engine closed the game by perpetual checks.

Approaching the halfway point, the match is still quite close. Stockfish has shown it can win, but can it close the gap to Komodo? My gut feeling: no it can't. We'll know in about two weeks at the most.

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