Monday, July 11, 2016

Season 9, stage2, rounds 19-21

Table after 21 rounds:

The draw rate is 97/168 (58%). The last three rounds have been more drawish. 
Komodo and Stockfish are still 0.5 points apart, Jonny is still unbeaten but Fire has lost against Nirvana, its first loss of the stage. In the race for 8th place Nirvana has improved its chances with this win and is now leading. With 9 rounds to go all four engines ranked 8-11 have a fighting chance. There are now 8 games in their internal crosstable, only one is decisive.

Some of the game highlights

Nirvana started with an eval advantage against Raptor, but the evals dropped back to zero later for both engines. Both kings were exposed and there was a possibility of a perpetual check. Nirvana gave a rook for a bishop but the evals did not move. Raptor kept trying to draw but Nirvana was playing to win. After queens were exchanged the two advanced passers were enough for a win in a RBN vs RRB position.

Jonny had a pair of knights against Vajolet2's pair of bishops, in a closed position where knights were much better. After locking the queen side Jonny sacrificed a knight to open the king side and expose the black king. Vajolet2 had to give the material back to defend but this left a RR vs RR position with Jonny two pawns up for the win.

In Andscacs - Houdini white had a space advantage and the black pieces had little room to move. Andscacs used its advantage to clear the black queen side pawns and create dangerous passers. After queens were exchanged Houdini was two pawns down, Andscacs won a third pawn before the game was stopped. This was the first opening where both engines won with white.

Chiron survived more than 75 moves playing black against Komodo, but then its position collapsed. I don't know if Chiron blundered or not, but Komodo managed to exchange pieces and get to a winning bishop ending with better pawns.

Houdini - Gull was by far the longest game of the stage so far with 219 moves and 5:44 hours of play. At first it seemed that Houdini was in some danger from Gull's attack on its king. However, the position became static and both engines were shuffling and the game became boring. The game was extended by pawn moves and exchanges until finally it was over. Thankfully there were no 50-move game changing blunders.

Stockfish created a pair of advanced passers in the center against Rybka, and this forced Rybka to give a bishop for 3 pawns to get rid of them. Although arithmetically material was equal, in practice this led to a N vs pawns ending for white and the extra piece was enough for winning.

Nirvana - Fire reached a rook ending quickly. Nirvana was a pawn up which usually is not enough, and it also had no tablebase support, which Fire had. Therefore it was quite a surprise when gradually Nirvana's eval increased, and after several pawn exchanges the position was a won 7-man position for white, and both the engines saw the win. Another opening with two wins by white.

Jonny - Stockfish was a draw without any incident, but there was some talk in the chat that Stockfish may have missed a win in the endgame. I wonder...

Ginkgo was defending with black against Gull, and it chose to give a queen for RB. At first it seemed it had a solid fortress, but when pawns started to be exchanged (Ginkgo blunder?) Gull's queen became more dominant. When Gull took two black pawns the game was over. Double white win opening again. 

Andscacs and Naum exchanged pieces quickly reaching a RN vs RN position. The white pieces were much more active, leading to a rook endgame with a pawn advantage for Andscacs. After taking another pawn the game was practically won for white. Andscacs with wins from both sides of this opening.

Featured game: Fire - Jonny
Stage 2, round 20
Link to game on TCEC

Fire - Jonny was a clash of the 3rd and 4th ranked engines of the stage, both unbeaten so far. Fire had an eval advantage but pieces were exchanged very quickly and a queen ending was reached.

Queen endings can be very hard to predict. Both engines started to advance passers, and with the support of a queen the passers were hard to stop. Then came the highlight of the match:

Four queens on the board !! So much firepower, so many ways to mate. However, since both engines had two queens whatever Fire tried in its attack Jonny could find a defense. In the end one pair of queens was exchanged, the evals went down as did the excitement, nothing but a draw.

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