Saturday, December 5, 2015

Season 8 superfinal, games 81-90

After 90 games in the Komodo-Stockfish superfinal match, Komodo is leading 8-2 with 80 draws. With 10 games left there is no question which engine is going to win. Cato's openings are now 5/24 decisive, quite a change comparing to the first 5/66 decisive games. Stockfish has managed to win a second time, a small consolation for all the games Komodo has shown its superioirity.

In game 81 there were many exchanges in the opening stage and by move 30 the queen side was cleared and the pieces left were RB vs RN. Komodo was a pawn up but there wasn't enough material to increase the advantage. The game was adjudicated shortly after the rooks were exchanged. In game 82 many pieces were exchanged as well. Stockfish sacrificed a bishop for two pawns to get a pair of connected passers, but Komodo responded by giving back the material to stop the pawns from marching.This led to a drawn RN vs RN ending.

In game 83 there was some drama not directly related to chess. It started with an eval advantage for Komodo which gradually grew. It got to a point where the trend was clear and both engines seemed to agree that Komodo is going to win. I had something to do and did not watch for a couple of hours, but when I came back the game was still going on, or rather it was replayed. Later I understood from the chat that the server crashed in a clearly winning position for Komodo. There were some angry Komodo fans, but the protest wasn't so loud because Komodo was leading 6-1 at this point - if it were Stockfish the noise would still be heard.
When game 83 was replayed Komodo again started with an eval advantage that grew to over 1. Komodo won a pawn in a complicated position.

The evals stayed about the same for the next 15 moves while there were many exchanges on the board. It was not clear if a single pawn would be sufficient for a win with this pawn structure and the remaining pieces.

After the rooks were exchanged the black DSB was very weak and the LSB could not afford to be exchanged, allowing Komodo to gain another pawn.

Now the game was over, Stockfish could not defend against the king side pawns without losing more on the queen side. So in the end Komodo won in the rematch and the server crash did not change the result. For game 84 Stockfish fans hoped that if Komodo could win twice in a row as white then perhaps Stockfish could as well.However, with Stockfish as white the evals went down very quickly and material was equal. Each engine had a passed pawn but neither was able to get an advantage in the game. When both sides started to shuffle the game was adjudicated. Komodo was at 7-1, a bit embarassing for Stockfish.

In game 85 the board was cleared very quickly leaving a lot of space for the heavy pieces, especially on the queen side where there was only one pawn left by move 22. On move 38 an endgame of RPP vs RP was reached which was theoretically drawn. Komodo kept an eval over 0.6 which meant the game would be played on for a long while. It took another 60 moves before the game was stopped. Game 86 started on a different path, with pawns blocking the center and pieces shuffling behind. There were opportunities for flank attacks but with equal material and both evals at 0 it seemed like a potential quick draw.

Then out of nowhere the evals became negative at about -0.9, Komodo was pressing on the king side and Stockfish defending. Another case of "shuffle to Komodo win" for this match? But where was the win coming from? Knights were exchanged and with so many pawns the heavy pieces had a hard time moving. Komodo was able to infiltrate white's ranks and to get a pawn advantage, but there was a long sequence of shuffling moves with no eval change, perhaps Stockfish is holding? After queens were exchanged Komodo started to improve its eval.

One pair of rooks was exchanged and the black king attacked the central white pawns. Stockfish's only asset was the passed a pawn but it was not enough.

There was no way for Stockfish to keep the a pawn or to defend against all of Komodo's pawns advancing. 8-1 for Komodo, unbelievable, inconceivable (as Inigo would say...).

Game 87 was very quiet, reaching a BNN vs BNN endgame on move 29. The pawns and pieces were gradually exchanged and the game reached a tablebase draw. In game 88 Stockfish started with a small eval advantage, but around move 20 it started to jump up to a level of 1.5, while Komodo remained skeptic. And then came the knight sacrifice.

We haven't seen such a move from Stockfish in a long time. Right away Komodo saw it was in trouble, with too many pieces on the queen side and a vulnerable king side. There came a beautiful series of moves, Stockfish opened the king side and forced a series of exchanges that left it two pawns ahead.

The game wasn't formally over for another 25 moves but there was no doubt that Stockfish would win, two pawns in the endgame is just too much at this level of play. This was a totally unexpected win for Stockfish. Not that 8-2 is a lot better than 8-1, but this is the style we love to see in Stockfish games, and Komodo doesn't usually allow this to happen.
Game 89 reached an RB vs RN endgame by move 28. Komodo's small eval advantage was gone after the rooks were exchanged, and the game turned into a queening race. Both engines queened a pawn which eventually led to a tablebase draw. Game 90 reached a RRN vs RRN position in move 24. Stockfish had a pawn advantage but weak pawn structure with two pairs of doubled pawns. Stockfish rooks were more active and the eval increased to 0.6. Komodo defended well and the evals remained constant until dropping to zero as the game winded down to another tablebase draw.

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