Season 20 league 1 after RR2

Standings after RR2

 

Half of the league is over. Ethereal and rofChade are currently leading but the score difference between 1st and 7th place is only 1.5 points, so anything can happen. The only thing I can say with some certainty is that Defenchess is weaker than the other engines in the league, though it too is only 3 points behind.

The openings in this league, chosen by Bastiaan Braams, are more biased than usual. As a result the expected result of a game is a white win, so far there have been 33 white wins, 22 draws and one very surprising black win. This is unusual for TCEC and changes the way we can assess the performance of the engines as the league progresses. Points are less relevant, a good score is a draw with black. The situation becomes clearer only when all the game pairs in a DRR have been played. 

This situation raises the issue of fairness, always a TCEC favourite topic. It seems the challenge for the engines in this league is not the same as that for the engines in other stages this season, or any past TCEC season. The game pairs and double round robins ensure all 8 engines are given the same test, but you could argue that using more balanced openings as usual would have given different results. On the other hand TCEC aims to entertain, not to provide a "true measure" of which engine is "better". Also, you have to admit that defense is an important part of chess. 

I feel a bit uncomfortable with the league. It changes my viewing experience because I have to change my expectations. The excitement of a decisive match is not the same when an engine is given a better starting position and manages to convert. I find it harder to praise an engine that manages to reduce a worse position into a boring draw. From a reporting point of view this requires a different approach, since a decisive game becomes interesting for the competition only in the context of a game pair.

Interesting games

Games 1+29, Xiphos - SlowChess: In game 1 Xiphos attacked on the queen side and went a pawn up. The engines exchanged pieces and the game reached an opposite color bishops ending, draw. In game 29 there were no exchanges until move 44, SlowChess had a small eval advantage after the position opened. Both kings became exposed, SlowChess managed to win in a slow and difficult QR vs QN ending two pawns down. 

Games 2+30, rofChade - Nemorino: In game 2 rofChade was 2 pawns up for a while, Nemorino exchanged pieces and reduced to a RB vs RB position with white a pawn up. Eventually the rooks were exchanged and the bishops were of opposite color, draw. In game 30 Nemorino went a pawn up but got nowhere and evals came down. In a RRB vs RRB position rofChade's eval went negative and gradually increased. It created a passer while giving two more pawns. Nemorino pushed a passer to the 7th rank, both engines had to be careful to prevent pawn promotions. Nemorino thought it was OK for a while but it overlooked some of rofChade's moves. The game reached a R vs RR position, white had 4 pawns but the extra rook was good for a win. Very unusual with these book openings to win in black.

Games 3+31, RubiChess - Igel: In game 3 the action was on the queen side initially. When RubiChess opened the king side and attacked the black king Igel reduced to a Q vs RB position and held the draw. In game 31 Igel managed to block the queen side and trap a black rook and bishop. In a QRN vs QRB position RubiChess was almost completely paralyzed, it gave a rook to free the bishop and lost quickly.

Games 6+34, Igel - Ethereal: In game 6 Igel opened a file on the queen side after some shuffling. The engines reduced to a RBN vs RBN position with white two pawns up. Eventually Ethereal was able to capture two pawns back but by then Igel had advanced connected passers. One passer queened and the game was soon over. In game 34 both engines had passers in the center. After a series of exchanges Igel captured the white passer and the game reached a RBN vs RR position. Ethereal thought it had an advantage with its eval over 2, Igel lost its passers but managed to capture all the white pawns. This left a drawn RN vs R ending.

Games 7+35, Nemorino - Rubichess: In game 7 RubiChess blundered in RR vs RN ending. It gave its knight thinking that the connected passers were strong enough as compensation. Nemorino found a way to stop the passers, and though it was left without pawns the extra rook gave it the win. In game 35 RubiChess had a passer on the 7th rank in a RRB vs RRN position, Nemorino reduced to a drawn rook ending.

Games 16+44, rofChade - RubiChess: It seemed that RubiChess equalized in game 16, reaching a QRB vs QRB position with evals close to 0. After RubiChess captured two pawns rofChade captured a rook for a bishop, then in a long endgame rofChade managed to reduce to a king and pawns endgame. The white king was able to block the black passers but the black king was too far to prevent a queening and a win for white. Game 44 was more straightforward. RubiChess attacked from the open queen side and eventually captured a bishop. A passer in a RBB vs RB position forced rofChade to lose another bishop and the game.

Games 17+45, RubiChess - SlowChess: In game 17 RubiChess went up a pawn early. The engines exchanged pieces until only RB vs RN were left, RubiChess captured another pawn and reduced to a winning rook ending. In game 45 material was equal. SlowChess tried to attack through the queen side but only managed a perpetual check draw.

Games 18+46, Ethereal - rofChade: Ethereal gave a rook for a knight in game 18, then pushed pawns in the center and reduced to a RN vs RR position. rofChade lost a rook trying to stop the pawns, Ethereal managed to promote to a queen and win. In game 46 Ethereal equalized quickly, after the position opened the engines exchanged pieces until reaching a tablebase draw.

Games 22+50, Xiphos - Igel: In game 22 Xiphos was up a pawn with a queen side passer from the start, but it did not push it forward. After a few exchanges Xiphos captured a second pawn and created connected passers. The engines reduced to a rook ending, the white king came forward and Igel couldn't prevent a queening, game over. In game 50 Igel was a pawn up but Xiphos managed to keep a protected pawn on the queen side. Igel couldn't create a passer, evals came down and the game was adjudicated quickly.

Games 25+53, Ethereal - SlowChess: In game 25 Ethereal captured a pawn and later created a passer on the queen side. Ethereal delayed exchanging queens until it was ready, after the exchange only RN vs RN remained. Ethereal captured another pawn and pushed its passers forward. SlowChess lost a rook for one passer, but couldn't stop the other and a white win. In game 53 SlowChess was a pawn up but without a passer. It gave a rook for a bishop and tried to threaten the black king. Ethereal kept its king safe, it gave the material back and evals came down. The game was adjudicated a few moves later.

Games 27+55, Igel - rofChade: Igel had a better pawn structure in a QR vs QR position in game 27, but its eval stayed below 2. Both engines created passers that promoted to a queen, the game reduced to a drawn queen ending. In game 55 rofChade played the middlegame better,  it was down a pawn in a BB vs BN position with a doubled passer on the queen side. Igel lost a bishop to stop the white passers, rofChade kept one pawn safe to win in a bishop vs pawns endgame.