Friday, November 25, 2016

Season 9 superfinal, games 37-44

After 44 games Stockfish leads 8-3 with 33 draws. Since the shocking 4-0 start of the match after 16 games the result has been 4-3 (including one contested win for Stockfish). Houdini needs a winning streak of its own to have a chance of winning this match, doesn't seem likely though.

Game 37 started with an exchange-fest, only RRB vs RRB remained by move 20. The engines shuffled for about 30 moves with a few pawn moves, Stockfish kept a small eval advantage. When the engines started to exchange pawns and pieces the evals dropped to 0, and the game reached a drawn rook ending.
In game 38 the pieces stayed on the board longer. Houdini had a small eval advantage that gradually decreased, until after about 30 moves it jumped up close to 0.8. Indeed after simplification Houdini was able to win a pawn in a RRN vs RRB position. It had two queen side passers while Stockfish had one in the center. Houdini tried hard but couldn't improve its position, one pawn was not enough. Stockfish exchanged pawns and a pair of rooks to get a drawn RN vs RB ending. The draws continue, 5 openings in a row.

Evals stayed very low in game 39, the engines were ready to declare a draw from move 23. After the queen side pawns were locked the game almost ended in 3-fold repetition, then it was almost adjudicated. The second 3-fold attempt was successful.
In game 40 the evals also stayed low. The pawn structure was different, the queen side pawns became static early in the game but Houdini had a passer in the center. After exchanging queens both engines focused their attention on this passer, eventually Houdini didn't have enough support and the pawn was captured. A few moves after that a draw was declared.

Game 41 was a miniature for this match, a 3-fold repetition draw after only 29 moves. After locking the king side pawns the engines ran out of ideas and shook hands. Game 42 was completely different. There were only a few exchanges, each engine kept its pieces behind its pawns. The evals stayed low and after the king side was blocked the game seemed to be heading for a long shuffle and a draw. Instead Houdini's eval jumped over 1 and Stockfish's eval also moved up.

Houdini had a space advantage and could plan how to break the pawn line while Stockfish could only wait. Houdini took some moves to arrange its pieces and then launched the attack. As a result the queen side opened up, all the minor pieces were gone and Houdini was a pawn up.

Evals started to climb as Houdini focused its efforts on the weak queen side pawns. For the price of two king side pawns Houdini cleared the queen side and created two passers. To finish the game Houdini exchanged two rooks for the black queen and the pawns started to march, leading to a won Q vs RR ending. Finally a win after 14 straight draws.

Game 43 started with an eval advantage for white, the engines castled in opposite directions and Stockfish had a pawn advantage on the king side. After queens were exchanged not many pieces were left on the board, Stockfish was a pawn up and the evals were at 0.8.

Houdini's king moved forward to help in stopping the white pawns. After several exchanges only RB vs RN were left. While the black king was in the king side Stockfish moved its pieces to the queen side, creating a passer.

Houdini finally took out the king side pawn that was a threat from the start, but its king was too far when Stockfish's queen side pawns started to march. It took some time but eventually Stockfish got one pawn to the 7th rank, enough for a win. Stockfish immediately strikes back after its previous loss.
The reverse game developed similarly, white had a pawn advantage on the king side and an eval advantage. However, in this game Stockfish opened up the queen side so that when the game reached a RN vs RB ending Houdini did not have any pawns there. Stockfish managed to get a draw without difficulty.

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