Stockfish wins the season 20 superfinal. The final result is 14-8 with 78 draws. As expected the last 10 games were the most biased. There were two openings with two white wins, Stockfish and Leela each won a game pair. As a result Stockfish's lead stayed at +6.
In this season's superfinal the openings were ordered by their expected bias from lowest to highest. Indeed after 30 games there were 28 draws, it would seem the decisive games 5-6 were evidence that the engines could find bias in an opening that was thought to be drawn. In the next 20 games Stockfish managed to win two game pairs, it led 3-1 at the half point. Leela started to win game pairs in the second half of the match, it managed to tie the score at 3-3 and then at 5-5 after 70 games. The next 20 games were all Stockfish however, it won 6 game pairs and led decisively by 11-5. There were 6 wins in the last 10 games, but each engine won 3 games and the lead did not change.
The lower leagues of the season were short 1DRR events, some of the races were close but I can't feel the excitment when the games fly by so quickly. This season introduced a league 4 after qualification, a total of 39 engines participated. Seer started from qualification and promoted 3 times to league 2, but there it stopped. League 1 was slightly longer, a 2DRR event with longer time controls. Ethereal finished first and returned to the premier division after it was relegated in season 19. The second qualifier was rofChade, beating Igel in a tiebreak. League 1 featured unusual openings which were much more biased than usual. The expected result in all games was a white win, and the object became drawing in black instead of the usual object - winning.
The premier division was a 4DRR event with the best 8 engines in TCEC competing. Stockfish and Leela were the clear favorites to win, they led from the start and had a private race for the top spot. In the end their scores were tied and Leela won by a tiebreak. Komodo was updated to KomodoDragon in season 20, including NNUE technology. This new version was much better than before, it finished a clear 3rd, ahead of AllieStein and Stoofvlees. Ethereal and ScorpioNN battled against relegation, it was a close race which ScorpioNN won in the final rounds. Ethereal and rofChade relegated back to league 1.
This season more CPU engines added NNUE and became stronger as a result. Stockfish, KomodoDragon and Igel are examples of this trend, it appears that engines using NNUE position evaluation combined with AB look ahead perform better.
There was a new tiebreak criterion introduced this season, the r-mobility. Roughly this measured how much an engine has restricted its opponent's movement, where mate is best (0 moves and in check), then stalemate (0 moves, not in check) and so on. This criterion was second in its importance after head-to-head score. There were several tiereak decisions that used this criterion, including the winner of the premier division and the 2nd place in league 1. I am not a fan of this criterion. It is not easily accessible since it depends on the whole game and not just its result (compared to "number of wins"). You could argue that it is more related to the character of the game, preferring games with many captures and mating attacks over quiet draws that end with many pieces on the board. However, an engine that escapes an attack by countering with perpetual check can get an r-mobility win. My feeling is that r-mobility tiebreak decisions were arbitrary, but perhaps not more arbitrary than any other criterion.
That's all I have for this season. I looked back at previous season summaries and found references to the corona virus going back to season 17. It is still with us and it doesn't appear to be going anywhere soon. First, many thanks go to the TCEC organizers for keeping the tournament going in these troubled times, giving all of us fans something interesting to do when so much around us is closed and not functioning properly. Second, I'll repeat what I wrote last season:
"Please take this seriously, avoid crowded places and unnecessary
contacts. Keep yourselves and your family safe. Governments may give bad
advice or act slowly, but our personal health depends mostly on our
personal behavior."
See you next season,
Go TCEC!!
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In game 91 Stockfish's eval started over 1, it started to increase after move 10 (only 4 moves after book). Leela remained calm for a while, but Stockfish surprised it with every move and on move 14 Leela's eval jumped over 2. The engines exchanged queens and Stockfish had a dangerous passer in the center.
In a series of exchanges Leela captured the white d pawn and the engines reduced to a BN vs R ending on move 29. Stockfish went a pawn up quickly, after a while the pawn trades continued and Leela lost its last pawn. In a 7-man position Leela refused to take a pawn and lose immediately, it took 10 more moves for mate.
In game 92 evals increased from the start. Leela chose a different path and gave a pawn. There were many early exchanges and the game reached a RBB vs RBB position on move 16.
Leela quickly regained the pawn, Stockfish had two isolated pawns on the queen side and it had to play defensively. Evals continued to increase, they were close to 5 when Leela moved its rook to the 7th rank. The engines exchanged a pair of bishops and Stockfish went a pawn up, but both engines knew Leela had the advantage.
The white king came forward and captured the black c pawn.Leela pushed its passer to c7, then captured the black a pawn. Stockfish couldn't block the white passers, a queeining was followed by mate. There were two white wins in this opening, Stockfish leads 12-6.
Games 93-94 started with a 23-ply book in the Sicililan Dragon, Yugoslav attack, with the engines castling in opposite directions. In game 93 Stockfish gave two pawns, there were many early exchanges that opened the king side and exposed the black king. Leela protected its king and evals came down. After a while Stockfish broke through the defenses, and the black king ran to the queen side while Stockfish regained the pawns. The game reduced to a RB vs RN position and was soon adjudicated. Game 94 started with the same move sequence and diverged on move 22. Leela did not go after the black king, instead it captured two pawns on the queen side. The engines started to shuffle and evals came down, without pawn moves the game was soon adjudicated.
Games 95-96 started with a 32-ply book in the Ruy Lopez Flohr system, the first 31 plys identical to games played in the Kasparov - Karpov match in 1990. In game 95 the engines played out a long PV agreement with many exchanges, leading to a RBN vs RBN position with white a pawn up. Stockfish's eval was close to 1, Leela's eval came down as it redcuced to a B vs N ending. All the black pieces were invisible to the bishop and Leela blocked the white king's approach with a knight and two pawns. Stockfish lowered its eval after 30 shuffling moves and the game was adjudicated.
In game 96 Leela did not play Stockfish's expected moves. Stockfish's eval was unstable, it thought for a long time and its eval dropped under 0.5 and then jumped back over 1. Stockfish gave a knight for two pawns and opened the center, then all rooks were exchanged. Evals were below 1 again for a while, then came up again. Stockfish thought for 15 minutes on move 33 and this time its eval jumped over 2.
Stockfish controlled the long diagonals with its bishops and it waited to see Leela's plan. Leela slowly arranged its pieces to control the central squares, then on move 46 it forced a queen exchange. Both evals were over 2 in a BBN vs BB position.
The endgame was very long, Stockfish created a pawn wall across the board with a bishop in the gap, Leela managed to get its knight behind the black pawns to the protected square on c5. The engines traded pawns, Stockfish cleared the black king side pawns and created connected passers, while Leela created an advanced passer on the queen side. On move 88 the engines traded N for B and the white passer reached the 7th rank. Leela captured a pawn and created a second passer, then gave a bishop and pushed another passer to the 7th rank. Leela promoted to a queen, Stockfish had 3 advanced passers but it was not enough to avoid mate. Leela wins the game pair, Stockfish leads 12-7.
Games 97-98 started with a 20-ply book in the Sicilian Najdorf, English attack, with the engines castled in opposite directions. In game 97 Stockfish pushed pawns on the king side while Leela concentrated its pieces on the queen side. A pawn trade opened the king side a little, Stockfish shifted its rooks to the center and doubled on the d file. Stockfish's eval increased as it targeted the black pawns on the queen side, Leela traded one for a white pawn on the king side. This gave Stockfish a passer in the center, its eval was over 3 while Leela felt safe.
Stockfish's eval kept increasing while Leela's eval stayed low, very unusual to see this happening. Leela doubled rooks on the h file and threatened the white queen but nothing came out of it. Stockfish managed to push its passer to d6 safely, but there Leela captured it a series of exchanges that left a QRB vs QRN position. Finally Leela's eval started to react, material was equal and Stockfish's advantage appeared to be the two isolated black pawns and the exposed black king.
Leela lost the d pawn after a few moves, then Stockfish used a mate threat to force a queen exchange. Leela gave the knight to clear the king side pawns and the RB vs R ending was a win for white.
Game 98 started similarly, Leela pushed pawns on the king side. Stockfish did not trade pawns, instead it locked the king side when a white pawn reached g6. The engines exchanged pieces until there were only RRN vs RRB left on move 33. Evals drifted down while the engines mostly shuffled until move 94. Several exchanges opened the queen side, evals were close to 0 and the game was adjudicated. Stockfish wins the game pair, it leads 13-7.
In game 99 there were almost no exchanges after the start except for a pair of bishops. The center was blocked, Stockfish castled long, it had a space advantage and an eval over 1. On move 26 Leela captured a pawn on the queen side, this allowed Stockfish to move a knight to c6. Leela felt quite safe when it captured the knight, Stockfish's eval jumped over 2 though it gave a second pawn. The king side opened and the black king was threatened. Stockfish took a pawn with a bishop, Leela took with a rook and expected Stockfish to retake. Leela's eval dropped close to 0, it didn't expect Stockfish's reaction.
Stockfish moved Rg6 and Leela's eval jumped immediately over 10!! Leela couldn't take with the pawn because that would open the h file for mate threats. Instead Leela gave its queen for a rook and the game quickly reduced to a Q vs RN ending.
The white king captured the remaining black pawns, Stockfish's win was just a matter of time.
In game 100 Leela decided to castle short. Stockfish developed its queen side slowly, Leela traded pawns there and then went a pawn up. Stockfish regained the pawn a few moves later but its eval jumped over 2 though material was equal.
There were too many weak black pawns and Stockfish's pieces were all passive defending them. Evals increased quickly as Stockfish gave a rook for a knight. It gave a pawn and tried to block the king side, Leela exchanged queens and reduced to a RR vs RN position.
Stockfish blocked the g pawn with its king, after Leela moved its king to e3 it forced a pawn trade with the f pawn. The black pawn wall crumbled and Leela created a passer in the center. Leela captured the black h pawn and pushed its king side passers. Stockfish couldn't hold against three passers on the 6th file, the game was soon over. There were two white wins in this opening, the final score is 14-8.
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