Tuesday, July 19, 2016

Season 9, stage2, rounds 25-27

Table after 27 rounds:

The draw rate is 121/216 (56%). 
Stockfish is now leading the table after closing the gap to Komodo with three straight wins.
In the race for 8th place Rybka beat Hannibal, a rare win both for Rybka and in games between 8th place contestants. This result puts it in front a full point ahead of Ginkgo. With three games remaining this could be enough. Remaining games are (underlined opponents playing black):
Rybka: Andscacs, Gull, Raptor
Ginkgo: Houdini, Raptor, Naum
Nirvana: Chiron, Hannibal, Andscacs
Hannibal: Jonny, Nirvana, Vajolet2

Some of the game highlights

Stockfish played the opening much better than Raptor. It was ahead a rook for a bishop in a RR vs RB position with evals at 4. Raptor had one last counter-measure, an advanced passer threatening to queen. Stockfish had no real problem getting rid of the black pawns before taking the passer and the bishop for a rook. The position was a 6-man won rook ending, but then there was a repeat of the Fire - Vajolet2 game: Stockfish played non-optimal moves and Raptor refused to give up. Sadly, this went on for 50 more moves before finally Raptor saw it was lost.

Fire had a space advantage against Houdini, the center and king side pawns were locked but Fire had a stronger queen side. The evals steadily increased as Fire created a 7th rank passer which was eventually turned into a bishop advantage for a win. Houdini had a big problem with this opening, losing from both sides.

Vajolet2's eval advantage against Ginkgo was quickly reduced to nothing, and then Ginkgo developed a strong king side attack. Starting with a knight sacrifice Ginkgo took out the white pawns defending the king. There followed a series of exchanges which resulted in a RBN vs RBN position with equal material. However, Ginkgo found a way to win (Vajolet2 blunder?) by exchanging down to create an unstoppable passer.

Jonny thought it had something against Komodo, even what appeared to be a solid pawn advantage. Komodo remained cool, defending and exchanging pieces until reaching a drawn rook ending. Jonny still doesn't have what it takes to beat Komodo.

Rybka went a pawn up early in the game against Protector. Many exchanges later and after a gradual eval increase the position was RN vs RB and Rybka won a second pawn. As the pawns marched the evals continued to increase, Protector had to lose a piece to avoid queening, losing the game.

There were many early exchanges in Gull - Chiron, and by move 30 the position was a N vs B endgame. Gull had more space and Chiron was playing defensively but the game was heading for a draw ... and then Chiron crashed yet again.

In Hannibal - Gull a complicated set of attacks and pins in the center was resolved into a bishop endgame with a pawn advantage for Gull. Hannibal thought it was losing immediately, perhaps giving up too soon, but Gull did find the win eventually.

Komodo couldn't find a weakness in Nirvana's position for almost 50 moves. When Nirvana made the crucial inaccuracy Komodo's evals started to increase rapidly. With clever queen maneuvers it won a pawn and created a passer. Nirvana couldn't defend its king and the queening threats, the game was soon over before we saw the actual collapse.

Naum - Vajolet2 was on the sure path to a draw. Naum had an eval advantage in a QBB vs QBN position but both engines were shuffling for many moves and the 50-move rule was getting close. After Vajolet2 moved a pawn Naum's eval started to increase. Naum found a way to get a pawn advantage and then exchange all pieces to get a won tablebase position. First win for Naum in this stage, all engines have at least one win this stage.

Houdini had a strong pawn attack on Raptor's king, resulting in a RB vs RB endgame with a pawn advantage for Houdini. The black king hid behind a white pawn but was also trapped as a result. When Houdini's king marched forward it made the difference, and the game reached a rook ending with two pawns advantage, and easy win for Houdini.

There were many early exchanges in Stockfish - Ginkgo and the game reached a RNN vs RNN position. For 35 moves the engines shuffled their pieces with almost no pawn moves, the game was clearly a draw. Ginkgo moved a pawn and Stockfish's eval jumped a little. Another inaccuracy and the evals started to rise fast. Through careful maneuvering Stockfish was able to exchange some pawns and get a crucial passer. Ginkgo was forced to lose a knight for the passer, leading to a RN vs R ending. For the final blow Stockfish gave back the material to reach a won king and pawns ending, really beautiful in the PV but not played out.

Fire only got a draw against Naum, Vajolet2 held a draw against Komodo. Disappointments for the top engines, Komodo slipped to second place behind Stockfish.

Nirvana won a rook for a bishop in the start against Protector. However after queens were exchanged it turned out that the black bishop pair was stronger than the extra white rook. Protector's eval started to climb as it managed to slowly take white pawns. In the open position Nirvana's king started to be in danger and Nirvana gave back a rook for a bishop, but then it was three pawns down. It took a while but Protector's win was inevitable. A blow to Nirvana's qualification chances.

Jonny had to settle for a draw against Chiron, another top engine disappointment.

Rybka - Hannibal had many imbalances and an intense struggle in the center, but after most pieces were exchanged the game reached a rook ending. The material was equal but Rybka had an eval advantage with its pawns more advanced. However, it was not clear whether the advantage was enough for a win. Indeed, after several pawn exchanges the position was a 7-man draw. Hannibal did not have tablebase support, and as a result it blundered and let Rybka win the endgame. Rybka is now first in the race for 8th.

Gull was up a bishop for pawns against Andscacs. The white king was exposed but it managed to escape perpetual check. Still the game appeared to be heading for a draw. Twice the TCEC draw rule was approached and missed at the last moment, Gull insisted it was slightly in the lead. Then suddenly it really was ahead, it got a pawn back and created a passer. After queens were exchanged in a RN vs R position the last white pawn proved unstoppable and cost Andscacs the rook, giving Gull the win.

Featured game: Houdini - Stockfish
Stage 2, round 26
Link to game on TCEC

The game started with an eval advantage for Houdini, but Stockfish equalized rather quickly. The first sign of trouble for Houdini came when it threatened to win a rook.

Stockfish thought the knight should be exchanged for the e6 bishop and was happy to take it with the d6 bishop even for a rook. Houdini then chose to leave the rook and took back the bishop. A bit strange, and an eval jump for Stockfish. Now Stockfish had strong central pawns, and the a5 bishop was in danger. A few moves later it found safety in the corner.

The bishop was completely trapped! After a long series of shuffles the game reached a QRB vs QRN position, with the bishop still trapped. Stockfish had time to arrange the attack and at the right moment the pawn advanced.

Houdini's position was in ruins, the bishop was free to move but Houdini had to face queening threats and defend its hanging pawns and its king. Stockfish won a pawn and after queen exchange won another.

Another beautiful win for Stockfish, the second win against Houdini in this stage.

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