Tuesday, April 17, 2018

Season 11 superfinal, games 91-100

The superfinal of season 11 is over, Stockfish beat Houdini 20-2 with 78 draws. This was one of the most one-sided superfinal matches in TCEC history.

There were a few exchanges at the start of game 91, Houdini gave an early pawn, the center was blocked and there was one open file on the queen side when the engines started to shuffle on move 29. After 70 moves the engines opened up the position, after exchanging queens the evals came down to 0. The game ended in a repetition with only pawns on the board. Evals were close to 0 in game 92. The position was more open and the engines gradually exchanged pieces until reaching a tablebase draw.

Game 93 started with Stockfish a pawn up and eval close to 1. After an early series of exchanges only RRB vs RRB remained on move 23, Stockfish had passers on the king side and Houdini had passers in the center. Both engines queened pawns and the game reached a tablebase draw. In game 94 Stockfish got the pawn back and evals were at 0 from move 20. Stockfish sacrificed a bishop and exposed the white king, Houdini traded down to a drawn rook ending.

Game 95 was a King's Gambit, a second variant of this opening in the superfinal. The white king was moving forward facing a black queen and two pawns. Houdini was a pawn up and had a small eval advantage. It chose to give back the pawn and exchange queens. Stockfish's king was awkward on the 3rd rank, yet it stayed safe. Stockfish exchanged all rooks leaving only BB vs BB, evals came down to 0. The game continued 40 more moves before draw adjudication.
In game 96 Stockfish didn't press on the king side, it patiently developed its pieces instead. Houdini regained the pawn by capturing on b7 with its queen, opening a file for a black rook. Both kings remained in the center, Stockfish's king side pawns looked intimidating.

Evals started to increase, first Houdini traded a rook for a knight and pawns, then Stockfish won a bishop for two more pawns. After exchanging queens only RN vs RRB remained, Houdini was 4 pawns up but playing a rook down against Stockfish is not a great idea...

The white king found safety behind its pawns, but it couldn't come out to help with the defense. Stockfish had an extra piece and it started to capture the white pawns. Its last pawn became a passer and started to march, ensuring a win for Stockfish.

In game 97 Stockfish started with an eval of around 1. The engines locked the center and shuffled for a while. Gradually the position opened up, first Houdini made a hole in the pawn line on the king side and then Stockfish opened two files on the queen side. After another shuffling period Stockfish gave a rook for a bishop and pawns and the engines traded down to a BB vs RB position. Stockfish's eval was above 1, it got a pawn to the 7th rank but Houdini gave the material back to get a drawn opposite color bishops ending. In game 98 Houdini kept a passer on the queen side, the center was locked and Stockfish concentrated forces on the king side. The engines were essentially shuffling from move 30, after 30 moves the engines exchanged a pair of rooks and continued shuffling. After avoiding the 50-move draw the engines traded down to a bishop ending and the game reached a tablebase draw.

Stockfish had an eval advantage starting game 99. The engines castled in opposite positions but did not push pawns forward. On move 31 Stockfish exchanged queens and created an advanced passer in the center, giving Houdini a similar passer though less advanced. Only RRN vs RRB remained and evals stayed under 1, the game seemed to be heading for a draw.

Stockfish had a pawn advantage on the queen side and it created another passer there. Houdini supported its passer with all pieces available, matching the white attacking pieces. Then Houdini allowed the white d pawn to reach d7 forcing a rook to move, Stockfish saw a winning line and its eval jumped over 3.

The win was not clear at first, the engines eliminated the passers in the center and exchanged minor pieces. Stockfish then took over the 7th rank with its rooks, captured a pawn and exposed the black king to attacks. Houdini had to be careful not to get into a mating net, Stockfish captured a second pawn and its queen pawns were free to march. The game was soon over.
Houdini started an attack on the black king with a knight sacrifice in game 100. Stockfish exchanged any piece it could, Houdini got the piece back and only RB vs RB remained with Houdini a pawn up on move 29. Evals were over 0.5, but after exchanging rooks the game reached an opposite color bishops ending, and the extra pawn was not enough. The engines continued to play for a hundred more moves before lowering evals enough for a draw. This was the last game of the season and the engines wanted to stay as long as they could.

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