Saturday, June 18, 2016

Season 9, stage 2, rounds 1-3

Now that the preliminary stage 1 is over, there are no more weak engines that hand out easy points. The competition in stage 2 is going to be much harder, who will finish in the top 8? This stage will have 8-move openings so there will be less opening blunders. This is a double RR, so each match will be played twice reversing the colors. This stage is then less about the openings and more about engine strength.

Table after 3 rounds:

The draw rate is18/24 (75%). The stage started with 12 draws in a row, and the fans were getting restless. There have been decisive games since then, but it looks like it's going to be a hard stage for all the engines.

Some of the game highlights

Komodo was a pawn up against Ginkgo, but Ginkgo's bishop pair was stronger than Komodo's pair of knights in the RNN vs RBB endgame. The evals jumped when Komodo won a rook for a knight, but with very few pawns left Ginkgo was able to hold the draw with its bishops.

In Chiron - Stockfish black went for an exchange of BN for RPP. For a while the evals were in Stockfish's favor, but Chiron was able to equalize. Stockfish gave material to get strong passers but Chiron was able to force a perpetual check for the draw.

Andscacs tried a rook for bishop exchange against Vajolet2, in order to break the pawn blockade. In the RB vs RR ending the pawns were taken until black had none. The game reached a drawn 6-man KBPP vs KR, but since both engines did not use tablebases the game continued for 60 more moves before adjudication.

Raptor used a nice combination in the game against Jonny, and got a QR vs QR ending with a pawn advantage. The evals were over 1 for a while, but Jonny had a pawn on the 2nd rank and an active queen, and that was enough to force a draw.

Nirvana gave a pawn against Rybka but couldn't get enough compensation for it. After most pieces were exchanged the position was a BN vs R endgame, Rybka a pawn up. The evals indicated Rybka had an advantage, with a passer guarded by the king and rook. But Nirvana managed to create a threat with its own passer, and when the two passers were exchanged the position became drawn. Did Rybka blunder a victory?

Vajolet2 and Gull reached a 3-fold repetition after 31 moves. This was the eleventh straight draw, frustrating.

Stockfish - Hannibal, first decisive game of the stage,  see featured game.

In Houdini - Chiron Houdini developed a strong attack on the black king that cost Chiron a knight for two pawns. From here it was a gradual increase in evals corresponding to pieces taken off the board and Houdini retaking pawns. Houdini was given the win in a RRN vs RR position with a pawn up. Two decisive games in a row, now the stage is officially open.

Ginkgo was a pawn up against Protector, in a position with a passer and with many pieces on the board. Protector defended well and refused to exchange pieces until very late in the game. When pieces started to come off the board the evals went down, the game ended in a tablebase draw.

Naum had an eval advantage out of the opening against Komodo, but Komodo was able to equalize and then to take the initiative. When the pieces were down to RBN vs RBN black's king side pawns were much better than white's queen side pawns. The game was adjudicated just before Naum started to lose material. Komodo with a first win, joining Stockfish and Houdini.

Komodo had an opening advantage against Raptor, but Raptor was able to equalize the position. Raptor was two pawns up (doubled passer) and Komodo had a bishop pair with evals close to zero. In the RBB vs RBN endgame Komodo was much better though and was soon clearly ahead. Raptor also failed to realize that the RP vs BP 6-man position reached was a win for Komodo due to the lack of tablebase support. Back to back wins for Komodo, best endgame expert in the field.

Rybka had a promising lead against Vajolet2, with two passed pawns on the queen side. Vajolet2 defended well, and was able to take one of the pawns. Rybka countered by exchanging the queen for two rooks, with evals getting closer to zero. With the second passer gone in a RRB vs QB position suddenly it was Rybka defending. The ending was a masterclass of how to use the queen's mobility in tight spaces. Vajolet2's queen almost singlehandedly won the game, taking out pawns while not allowing Rybka to move pieces. A surprising win for the new engine.

Jonny had an eval advantage out of the opening against Nirvana, and it was able to convert it into a winning RB vs RN endgame. It will be interesting to see whether Nirvana can win the rematch as easily.

Featured game: Stockfish - Hannibal
Stage 2, round 2
Link to game on TCEC

Stockfish had an eval advantage after the opening, but after so many draws there were doubts that any engine could get a real win. Hannibal had a bishop pair against Stockfish's knights, but the knights were holding the center and much more active.

With a pawn attack Stockfish opened the king side, exchanging a knight for a bishop in the process. Now both kings were exposed but Stockfish had the initiative and was clearly ahead on eval.

After exchanging queens Stockfish reached a winning RN vs RB endgame, with the black pawns weak and vulnerable. Also notable is how all the white pieces were on dark squares, invisible to the black bishop.

Hannibal went for a final move combination that resulted in a 6-man rook ending with white a+b pawns. With no tablebase support it was unaware this was winning for white, and for 9 moves Hannibal's eval was a draw. Losing came as quite a shock...

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