Wednesday, November 18, 2015

Season 8 superfinal, games 21-30

After 30 games in the Komodo-Stockfish superfinal match Komodo is leading by 2 wins with 28 draws. The last 10 games have all been draws, but one of them was the most dramatic game of the season that everybody is talking about  in the chat and Stockfish forums ever since.

Game 21 started with a small eval advantage for Komodo. After a series of 11 consecutive capures the remaining pieces were QRR vs QRR with many pawns. This is a sure sign of a draw. Once the queens were off the evals reached 0 and the pawns were gradually removed until a tablebase draw was reached.
The reverse game 22 was a totally different story. The pieces stayed on the board for a longer time in a complicated position. The evals started to jump after Komodo went for a skewer attack with a bishop.

Really difficult to understand what is going on with all the pins and threats, but white could be losing an exchange immediately. And yet Stockfish's eval went up as pieces started to fall. After a while things settled down a bit.

Stockfish was an exchange down, but it was quite optimistic according to the eval. Was it seeing something that Komodo missed? The queen side pawns had potential but was this enough? It should be noted that the website was down for over three hours, so nobody saw the game live at this stage. The white eval gradually increased and Komodo's eval started to agree with this as well. When the live broadcast returned the Stockfish fans started to get excited, it looked like the first Stockfish win is near. The evals started to jump when rooks were exchanged.

Stockfish was over the 6.5 eval threshold a few moves later, having established a pair of connected passed pawns.

Komodo was still behind in eval but was rising as well. It was just a matter of time... Stockfish just had to be careful of potential check threats but it had it covered in the PV at least. Then - the website went offline again. So close to the end, it was clear that we won't see it live but the win was sure. When the website returned though - A DRAW, WHAT??? Nobody could believe it. The evals were over 26 for Stockfish and almost 5 for Komodo, and then Stockfish threw it away in this position:

The move played was Kg4, allowing Komodo to escape with checks. The post game consensus was that Bc2, which appeared in the Stockfish PV a few moves back, was a sure win. Nobody could explain this choice by Stockfish and the shock was total. The Stockfish eval function became a joke, and the overall feeling was that if it can't convert an eval of 26 then how will it win games at all in this match?

In game 23 Komodo had an isolated passed pawn but it was not enough for a win in the RB vs RB ending that was reached. In game 24 again Komodo had an isolated passed pawn, this time as black, this time the ending was of opposite colored bishops. The draw took a surprisingly long time, Stockfish kept its eval at 0.06 not allowing the adjudication rule to be applied.

Game 25 reached an RB vs RB ending on move 20. I don't know why the evals stayed positive, perhaps because white won a pawn later, but before long the evals dropped to zero resulting in a draw. In game 26 Stockfish managed to create an eval advantage of 0.6, Komodo's pieces had very little room to move. However, there didn't seem to be a plan for Stockfish to improve and then pieces started to be taken off. The rook ending was again a dead draw.

In game 27 Komodo seemed to have a promising attack on the black king but Stockfish countered on the queen side, sacrificed a bishop for pawns and got a perpetual check draw. In game 28 the evals dropped to zero much faster and the game reached a repetition without a lot of action.

In game 29 the line the engines chose led to a material imbalance of BN vs RP. Komodo had a small eval advantage of 0.5 that made Stockfish fans nervous again.

Stockfish managed to capture a bishop, at the price of letting Komodo queen a pawn which cost a rook.

In the ending Komodo's extra bishop let it eliminate some of the black pawns, but when all the white pawns were off the board the game was drawn. In game 30 Stockfish had a small advantage but the game progressed without material imbalances. towards the end Komodo sacrificed two pawns to open the white king position, and the game was adjudicated just before the perpetual checks started.

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