Friday, April 13, 2018

Season 11 superfinal, games 71-80

After 80 games Stockfish leads 17-2 with 61 draws. Houdini finally got its 2nd win, this time drawing the reverse game. Stockfish still has a 15 win advantage, and with 20 more games to play it only needs a few more draws to be declared the winner of the superfinal.

Stockfish had an eval close to 1 at the start of game 71. Both engines attacked the opposite kings and after several exchanges the net outcome was that Stockfish was up a rook for a knight and pawn on move 23. Houdini's king was exposed and evals started to increase in a QRB vs QBB position. After exchanging queens Houdini had passers in the center and Stockfish had a doubled passer on the king side. Houdini managed to get a pawn to the 2nd rank protected by a bishop. It couldn't promote but Stockfish had to keep its rook guarding the file. Stockfish's evals was over 2 for a while but it soon realised Houdini was holding. After many moves Stockfish released the black pawn to promote to a queen, and the game ended in a RB vs Q draw. Another narrow escape for Houdini, seems this is the best it can do to show its strength. In game 72 Stockfish equalized quickly and Houdini's eval dropped on move 24. The engines were mostly shuffling with most pawns on the board. Houdini broke through the center, leading to many exchanges and a drawn rook ending.

Many early exchanges in game 73 left RRB vs RRB on move 32 and evals close to 0. The engines continued to exchange pawns and pieces until reaching a tablebase draw. In game 74 evals were negative for a while but Houdini was never in any danger. After exchanging queens the game reached a RB vs RB position. Both engines had advanced passers, Stockfish gave a rook to stop the black passer, Houdini forced a perpetual check draw ro avoid the queening of a white passer.

Stockfish's eval climbed above 1 at the start of game 75. The engines castled in opposite directions, there were many early exchanges and queens were off as well. Houdini didn't seem to be worse on the board, material was equal and the pawns structures were similar.

Stockfish used its bishop to block the king side and apply pressure on the black king, together with a rook on the 7th rank. The evals slowly increased, then suddenly jumped above 2.5. Houdini moved a rook on the back rank to d8 and not g8 as Stockfish recommended, Stockfish played the same response it planned and doubled rooks on the e file.

Houdini gave a rook to take out the white bishop, and the evals jumped higher very quickly. The game reached a RR vs RN position, the white pawns on the queen side started to march and Houdini saw it couldn't stop them in the long run.
In game 76 both engines castled long, evals stayed close to 0. After exchanging most pieces only RB vs RB were left on move 31 and the game ended in a tablebase draw not long afterwards.

Stockfish had an eval advantage of about 1 in game 77. The engines castled in opposite directions, both engines pushed pawns towards the opposing king and opened files. Stockfish's eval peaked close to 2, it attacked on the king side and exposed the black king. However the eval had a sudden drop, Houdini's counter on the queen side exposed the white king and was enough for a perpetual check draw.
Houdini had an eval advantage in game 78. Stockfish delayed castling its king until after queens were exchanged. On move 30 only RRB vs RRB remained with equal material. Evals hadn't moved a lot since the opening, probably a draw.

Houdini captured a pawn and the engines exchanged a pair of rooks. It was not clear how Houdini can improve its position, and the bishops of opposite color made the position look drawish. Yet the evals slowly crept up. Houdini managed to capture a second pawn and create a passer on the king side. Could this be Houdini's day?

Houdini secured its passer and then moved its rook forward where it could attack the black king and threaten the queen side pawns. Stockfish was forced to exchange rooks and then it saw a win for Houdini. Houdini took a few more moves to realise that despite the opposite color bishops ending it had a winning position.

With two passers and the king on its way to the queen side Houdini was too strong and Stockfish agreed it was a win for white. Finally an opening where Houdini wins a game and does not lose on the reverse.

Game 79 had a wild start. The king side remained undeveloped and both engines kept their kings in the center uncastled. Stockfish pushed two pawns on the queen side and one got to the 7th rank. Houdini arranged its pieces for an attack on the white king, with the pawn on a3 blocking the escape route. Stockfish's eval was over 1 but changed very little.

Both queens attacked simultaneously, and both kings looked very vulnerable. Stockfish queened its pawn and for a while played with two queens. Houdini's mate threat kept it alive, forcing white to lose one of the queens. After a series of exchanges the remaining queens were gone and the attacks were over, Stockfish had a material advantage with RRN vs RBB remaining.

The engines exchanged a pair of rooks and the evals increased slowly. It is possible that Houdini could have held, but Stockfish found a way to improve and its evals started to jump. As usual Houdini realised it was in trouble a few moves later. The black bishop pair was harassed by the white rook, allowing Stockfish to arrange its pieces and keep the black king away. 

The white pawn started to march and the game was soon over. Houdini couldn't stop it without losing material. What a game!
 In game 80 both kings remained uncastled, but both engines kept their pieces behind the pawn lines and did not attack. The engines started to shuffle with almost all pieces on the board. On move 32 the pawn lines locked across the board, with only the f pawns able to move. Nothing happened for the next 75 moves, except a few f pawn moves and a few piece exchanges. To finish the game the engines opened up the king side and exchanged all pieces but a pair of knights.

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