Friday, April 6, 2018

Season 11 superfinal, games 31-40

After 40 games Stockfish leads 11-1 with 28 draws. Houdini finally achieved its first win. Stockfish won the same opening as white, perhaps the opening was too biased. The match continues to be one-sided, though there were a few more draws compared to the previous two games.

Stockfish had a small eval advantage from the start of game 31. The center was blocked and all pieces were on the board. Stockfish had more space on the king side, its king a little exposed. Houdini was better on the queen side, but its king had little support from the black pieces due to the pawn wall. Stockfish's queen side rook looked awkward, blocked by its own bishop.

Stockfish sacrificed a bishop for pawns to expose the black king, its eval jumped above 2. Houdini countered by opening the queen side and attacking the white king. The white back ranks were weak and Houdini's pieces drove the white king forward. However, the black king was in grave danger, once the checks stopped Stockfish sent a knight to join the attack, offering a rook to Houdini.

Stockfish was RB down, but it had the black king in a mating net. Houdini had to give its queen to stay alive, and with three passers and a queen facing the black king Stockfish was about to gain more material when the game was adjudicated. A spectacular win in 36 moves.
Game 32 started with evals close to 0. Stockfish kept its king uncastled in the center, it gave a pawn to open a file for its king side rook. On the queen side Stockfish had a pawn advantage and a strong knight.

Houdini's eval started to increase gradually. It got rid of the white queen side knight and gave the pawn back. Stockfish had a pawn majority on the queen side, while Houdini created a passer in the center with support from behind. Evals were close to 2, could this be Houdini's first win?

Houdini formed a pawn line on the king side and secured its passer. Stockfish gave a pawn in the center to try and threaten the exposed white king, Houdini exchanged pieces until only RN vs RB remained, evals over 3.5.

Stockfish had to keep an eye on the d pawn, allowing Houdini's king to walk to the queen side. With the additional piece Houdini started to capture the black pawns on queen side and the game was soon adjudicated. A win for Houdini, finally. Stockfish won the previous game so the opening is also a factor.

In game 33 Houdini gave a rook for a bishop early in the game. Stockfish had an eval close to 1 and the engines started to shuffle on move 22. A few pawn moves and exchanges got the engines to move 100 with the 50-move counter down to 1, but Stockfish avoided the draw and opened the position. The game continued for another 25 moves, reaching a queen ending and a perpetual check draw. Game 34 started with early exchanges, the engines started to stabilize and shuffle from move 16. Stockfish concentrated forces on the king side and evals became negative for a while. Houdini just traded all the pieces and got a drawn rook ending. After 6 openings with decisive results we finally got back to "normal" with two draws in a row.

Stockfish started game 35 with a small eval advantage. After a while the evals started to increase, the reason was not evident at first. Houdini had a central passer while Stockfish had a pawn majority on the queen side. The black LSB was trapped on the queen side.

Stockfish pushed its queen side pawns forward and created two connected passers. Houdini started a series of exchanges, with a net result of being a rook for a knight up in a RBN vs RRB position. However Stockfish had a pawn on the 7th rank. 

Stockfish advanced with a second pawn and Houdini was forced to lose a rook to stop the two passers. The game reached a RB vs R ending, Houdini two pawns up. Evals were over 3 and climbing.

Stockfish took its time and slowly captured the black pawns. After 15 moves the game was over. 
Evals stayed low in game 36. The engines exchanged queens on move 27 and the game reached a RN vs RN position on move 32. The engines continued to trade, the game ended in a quick tablebase draw.

Stockfish kept its king uncastled in game 37. It created an advanced passer in the center and Houdini was concentrated on stopping it and did not attack the exposed white king. After most pieces were exchanged Houdini got rid of the passer, and the game reached a drawn tablebase position. In game 38 there were many early exchanges and only RN vs RB remained after move 21. Evals dropped to 0 quickly and the game was adjudicated.

Game 39 started with Stockfish a pawn up. Stockfish's eval stayed below 1. After queens were exchanged the engines stablized the pawn lines. Then all the rooks were traded off and the engines started to shuffle in a BN vs BN position. It took more than 40 moves for Stockfish to lower its eval enough for the draw rule to apply. There were many early exchanges in game 40. The game reached a RR vs RR position on move 27, Houdini still a pawn up. Evals dropped to 0, Stockfish regained the pawn and the game reached a drawn rook ending.

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