Sunday, December 4, 2016

Season 9 superfinal, games 71-76

After 76 games Stockfish is leading 13-7 with 56 draws. With 24 games to go Stockfish will almost certainly win the match. Houdini seems to have an advantage only in long games with time running out, and this doesn't happen very often.

Game 71 started with an eval advantage for Stockfish. There were many early exchanges and the game reached a RRN vs RRN position after 23 moves.

Houdini's queen side pawns were weak but the position looked defendable, not a lot Stockfish could try. Nevertheless as the game continued Stockfish's eval started to climb, it definitely saw something. At the right moment Stockfish played f5, temporarily losing a pawn and disrupting the black pawn structure.

After exchanging a pair of rooks and capturing a few pawns the white h pawn became a passer and Houdini had to keep an eye on it so it couldn't promote.

From here it was an easy win for Stockfish, Houdini was forced to lose the knight to get rid of the h pawn, and Stockfish could use the material advantage to win using the queen side pawns. Stockfish goes +7 again.
There were less exchanges after the opening of game 72, and after queens were exchanged the pawn lines became static and the engines started to shuffle.

Apart from a few pawn moves and the exchange of a pair of knights nothing happened in the game. The evals climbed above 1.5, Houdini had a space advantage and it had a few pawn moves it could make that would break the black pawn line, but it chose to wait.

The engines continued to shuffle for another 35 moves. They were getting low on time and the game entered blitz mode. Houdini opened up the queen side and brought its king to the center. After exchanging a knight for a bishop Houdini's eval started to increase. It created a passer on the queen side and exchaged down to a rook ending.

Stockfish could not stop the passer without allowing the white king to infiltrate the king side and attack the black pawns. This is the second time Houdini won by waiting for Stockfish to be low on time. Both games of this opening were a win for white, but with very different winning strategies. The lead is back to +6.

In game 73 Stockfish attacked with its king side pawns, leaving the king a little exposed. However the center was blocked and the white king was not in any danger. Houdini formed a defensive line across the board, and evals climbed above 1 when it gave a rook for one of the white bishops. After exchanging queens only RRB vs RBN remained, and Stockfish continued to shuffle since it couldn't break Houdini's line. The game was adjudicated a draw when both engines lowered their evals enough.
In the reverse game Houdini kept its king side pawns near the king, The center was wide open, white had a pawn advantage on the king side, black on the queen side. After a series of exchanges only RB vs RB remained. Houdini managed to be a pawn up but with opposite color bishops this wasn't enough to secure a win.

All the pawns were still on the board until move 25 in game 75. There were a few moves where Houdini's eval was in its favor as black, a rare event in this match. Houdini had a space advantage but nothing more, its eval got back to 0 and stayed close to it for the rest of the game. After opening a few files the engines exchanged all rooks and then shuffled until a draw was agreed.
In game 76 Stockfish seemed to develop a dangerous attack on the white king on the queen side, with the king exposed and facing a QR combination. Stockfish's eval was a constant 0 though, so it didn't believe the attack was effective. Indeed the engines exchanged pieces until only the kings and pawns were left, and draw a few moves later.

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