Saturday, July 4, 2020

Season 18 superfinal statistics

A summary statistics table of previous stages and seasons. 

Draw rate, wins

Final draw rate was 61%.

Game termination

The three most common game termination causes were:

51% - TCEC draw rule
37% - TCEC win rule
5% - SyzygyTB, 3-Fold repetition

There were no crashes in the stage.

Moves per game
Median= 64.3
Average= 75.6

There were 16 games longer than 100 moves, the longest was 357 moves (Leela - Stockfish, game 73, draw).

Time per game (hours)

Median= 3:14
Average= 3:08

Openings

There were variable length book openings in this stage chosen by Jeroen. The first letter of the ECO codes was distributed as follows:
The engines had almost no freedom to choose the opening variant, 96% of the game pairs repeated the same ECO code and opening variant. In all the game pairs the ECO first letter was repeated twice. The two exceptions were a few very short book sequences of length under 5.

Reverse pairs, wins
There was an unusual high number of 1-1 results with two white wins, Jeroen's openings were designed to be more biased than usual.

Reverse pairs, same moves
Pairs of reverse games diverged very quickly, 36% diverged immediately out of book, 72% of the pairs diverged at most after 1 move. The longest repeated sequence of moves was 12 plys (Leela - Stockfish games 87 and 88, KGA Quaade gambit, Stockfish wins as white)

Season 18 superfinal games 71-80

After 80 games Stockfish leads 19-14 with 47 draws. Leela won twice, and twice Stockfish won the reverse game. Then Stockfish won a game pair and increased the lead to +5. Only 20 games left, It is very likely that Stockfish will win the match.

Games 71-72 started with the Latvian gambit with a significant advantage for white. In game 71 Leela went a pawn up and queens were off early. Evals increased as the engines developed their pieces, a series of exchanges led to a RRB vs RRB position on move 21.


Leela had a pawn majority on the king side, after exchanging a pair of rooks Leela moved its remaining rook forward to attack the pawns on the queen side. Stockfish tried to defend the pawns and kept the white king away, eventually Leela managed to capture a pawn. 


Once the white pawns started to advance the material advantage was enough for a win. 

In game 72 Leela castled short despite a hole in the pawn protection. On move 12 Stockfish's eval jumped over 3, it sacrificed a bishop and exposed the black king, attacking with its queen and two knights.


The black king was in danger of being mated, Leela had to give a rook for a knight but still the attack wasn't over. Stockfish created a passer and pushed it forward to the 7th rank.


Leela lost a rook to stop the passer, after exchanging queens the game reached a RR vs BN position. Leela's still had an advanced passer, Stockfish lost some material for it but the R vs N ending was a win. There were two white wins in this opening, Stockfish's lead is still +4.

In game 73 there was a few minor piece and one pair of pawns exchanged after the start, the engines played behind long pawn lines. On move 30 the pawns stopped moving and shuffling began. Evals were over 1, Leela's eval peaked at 2, but there was no progress. Leela reset the 50 move counter on moves 77, 125, 171 and 220, then the position opened up and the engines reduced to a RRB vs RRB position. There were a few more exchanges until the end of the game on move 357, close but not a record length for TCEC. In game 74 again there were a few minor piece exchanges after the start, all pawns were on the board until Leela grabbed a pawn on move 19. The engines shuffled for a while and evals came down. The position opened, the white queen moved forward and Stockfish went a pawn up. Leela countered against the white king and captured a rook for a bishop. After exchanging queens Stockfish ended the game in a repetition. 

The engines exchanged most minor pieces early in game 75, evals steadily increased. Leela pushed pawns on the queen side where it had a pawn majority, one pawn made it to the 6th rank. It added a bishop on the 7th rank and Stockfish decided to give a rook and remove both the pawn and the bishop. Only QRR vs QRN were left and evals jumped over 2.5.


Evals continued to increase over 3, but Leela seemed to hesitate and shuffle. The queen side was stable and the focus needed to shift to the king side, however Leela waited for Stockfish to move a pawn and Stockfish wouldn't. The engines entered blitz mode, Leela pushed a pawn to avoid the a 50-move draw. Finally on move 85 Leela threatened mate and forced Stockfish to move the f pawn. After more shuffling Leela's queen moved forward and the white pawns opened the king side. The engines exchanged queens and evals jumped over 6.


The engines traded pawns and Leela created a passer on the queen side. The passer was close to promotion when the game was adjudicated. 

In game 76 the engines cleared the center and Leela went a pawn up. Nevertheless Stockfish's eval was over 1 and slowly increasing, the black king was stuck in the center and Leela decided not to castle and to move it to the king side out of the open center files. On move 24 the game reached a QRR vs QRR position.


Stockfish doubled rooks on the 7th rank, it regained the pawn and after exchanging a pair of rooks it went a pawn up. Stockfish's eval continued to increase while Leela thought it was relatively safe. The engines cleared all the queen side pawns, exchanged rooks and Stockfish captured another pawn to go 2 pawns up in a queen ending.


Stockfish already saw the win, Leela was still hopeful. Leela got one pawn back but the white pawns started to advance and Leela's eval increased as well. Both engines raced with their pawns, both were a square away from promotion. Stockfish's queen kept the black king away from both pawns, so it could stop the black pawn and promote its own. Another opening with two white wins, Stockfish's lead is still +4.

Games 77-78 started with a 20-ply book in the English oening, Symmetrical variation where the black queen moved forward and the white king was forced to move. In both games the immediate continuation involved the white knight forcing the black king to move and capturing a rook with a fork.In game 77 Stockfish's eval jumped on move 17, it drove the white king to the queen side edge and a pair of doubled pawns trapped it there, a kind of vertical "back rank". Stockfish did not take back the knight until move 25, its eval was already over (negative) 3.


Leela captured the pinned black knight but it had to be careful not to get mated. The white bishop was close to being trapped and Leela gave a rook for a bishop to let it out. In a QRB vs QR position Stockfish was 3 pawns up, the black rook joined the attack and again Leela king was in danger. Leela lost material to escape, the game reduced to a rook ending. 


Stockfish was two pawns up, the king side pawns advanced and Leela couldn't stop them. 

Stockfish's eval was 0 from move 15 till the end of game 78. The white king found safety on a2, after Leela took the knight in the corner the engines exchanged most pieces and the game reached a rook ending on move 29. Stockfish pushed a passer to the 7th rank, Leela pushed a passer to the 2nd rank with king support. Both engines could not promote their pawn and they shuffled until Leela lowered its eval for the draw rule on move 78. Stockfish wins the game pair and its lead increases to +5.

There were only a few exchanges after the start of game 79, the center was crowded and Leela tried to push through the queen side. Stockfish placed a knight on e3 that limited the movement of the white pieces. On move 33 a file opened on the queen side and the engines exchanged all rooks throught it, leading to a QB vs QB position. Stockfish's eval came down to 0, Leela had an advanced passer but its exposed king was vulnerable to checks. Leela sacrificed a bishop and went on the attack, after it captured the black bishop Stockfish ended the game in perpetual check. In game 80 Stockfish opened a file on the queen side and moved a rook to the 7th rank .Leela countered on the king side and a series of exchanges reduced to a RB vs RB position on move 29. Stockfish was a pawn up, its eval jumped to 1.5 when it pushed a passer to the 6th rank. It was a false alarm as Leela reduced to an opposite color bishop ending. Stockfish kept the game going until move 121.

Thursday, July 2, 2020

Season 18 superfinal games 61-70

After 70 games Stockfish leads 16-12 with 42 draws. Leela fought back and won two game pairs after a long drought (last game pair Leela won was in games 33-34). Stockfish added another game pair to keep the lead at +4. There are only 30 games left, Leela needs wins to stay in the match.

Leela kept its king in the center and pushed pawns on the king side in game 61. Leela had a space advantage, the center was blocked and the black pieces had little room to move. Stockfish moved its queen forward but Leela wouldn't exchange queens. Leela placed a knight on e6 and trapped a black rook, evals were over 2 on move 25.


Stockfish played f6 in an attempt to open some space for its pieces, this opened a path for the white bishop to move behind the pawns via d8 and attack on the queen side. Leela captured a pawn and then found an outpost for the bishop on b6 supported by a pawn. On the king side Leela targeted the g6 pawn.


The engines exchanged queens and Leela went two pawns up, then the game reached a RB vs RB ending. When Leela captured another pawn the game was adjudicated.

There were no castlings in game 62, both kings walked to the king side. All pawns remained on the board until move 23, the engines played behind the pawn lines. Stockfish's eval was over 1 but evals were constant, after locking the king side pawns it seemed the engines shuffled and had no plan. 
Around move 45 evals started to increase, Stockfish saw something but it wasn't clear what that was. Stockfish moved pieces to the queen side and targeted the black b6 pawn.


The white bishop interfered with Leela's heavy pieces that tried to protect the b6 pawn. Stockfish shifted to the king side quickly, opened the block with f4 and attacked with its queen. Leela was caught off guard with its heavy pieces too far to help. Stockfish gave a rook for one of the knights, the black king was in serious danger..


Stockfish captured the weak black passer and blocked Leela's queen route to the king side. Only one black rook came to help the king and that wasn't sufficient, the game was adjudicated as Leela lost material and Stockfish saw the mate coming. There were two white wins in this opening, lead is still +5.

The center was blocked in game 63, all pawns and pieces remained on the board in the first 21 moves. Stockfish castled long and it dominated the queen side, while Leela concentrated forces on the king side. There was one minor piece exchange and the engines started to shuffle, evals were around 1.5 and didn't change for a long time. Only on move 63 Leela moved a pawn to open the king side, Stockfish's eval immediately jumped over 3. 


The effect of the long shuffle was that the rest of the game was played in blitz. Leela captured the h6 pawn and created a 3 to 1 pawn majority on the king side. Stockfish captured a pawn in the center but it gave a rook to stop all the advancing white pawns. After exchanging queens Stockfish tried to build a fortress for its king.


Leela started to shuffle again, evals increased and the game was adjudicated. We didn't get to see how Leela could win but it was a rook up so there probably was a way.

In game 64 Stockfish opened the king side immediately and forced the black king to move. Stockfish castled long and both kings were on the queen side. On move 23 Leela gave a pawn, leading to a series of exchanges including queens that opened the board. Evals came down and the engines continued to exchange pieces, the game reached a drawn rook ending. Leela wins the game pair, Stockfish's lead is reduced to +4.

Stockfish grabbed a pawn early in game 65, allowing Leela to move a bishop to h6 and trap the king. Stockfish then captured a second pawn, evals were positive though as the white pieces were better developed. On move 20 Stockfish attacked the white queen, and Leela surprised with sacrificing the queen for a knight and a bishop. Leela's eval jumped right away, Stockfish's reacted only two moves later. Leela could have gained some of the material back, but with the black king trapped in the corner Leela preferred to keep its attack going.


The black bishop was pinned and was attacked and defended by 3 pieces. Leela moved its free knight forward, and after a few shuffle moves it captured the e6 pawn. Stockfish captured the knight and lost its bishop, the black king used the opportunity to escape from the corner. However, it only managed to move to a new trap on f6, and Leela used a mate threat to capture the white queen for a rook.


The black king was fully boxed in by its own pawns and the white bishop, knight and pawn. The rook on e6 could not move because of immediate mate. Leela waited a few moves without taking it, Stockfish moved its other rook forward to take the f4 pawn but it lost a rook and the game.

In game 66 Stockfish did not castle and its rook protected the h pawn. The engines exchanged pawns and opened the center, another series of exchanges reduced to a double rook ending on move 29. Stockifsh was a pawn up and evals were close to 0. Leela regained the pawn, the engines exchanged a pair of rooks and the game was adjudicated. Leela wins another game pair and Stockfish's lead is now +3.

Both engines castled long in game 67. The black king was a little more exposed, there were many exchanges on the queen side and on move 26 the game reached a QRR vs QRR position. Stckfish's eval came down to 0, the engines shuffled for 20 moves. After trading several pawns and a pair of rooks shuffling resumed and the game was adjudicated.

The engines again castled long in game 68. There were many early exchanges, mostly on the king side, and the game reached a QRN vs QRN position on move 25. The black king was more exposed, Stockfish's eval slowly increased and it was over 2 when the engines exchanged a pair of pawns on the queen side. Stockfish found a safe square for its king, after another pawn trade Stockfish opened a file on the queen side and its eval went over 4.


The white queen and rook could get from one side of the board to the other side very quickly. They chased the black king to the king side and then back to the center. The net result was a very similar position except that the rook and queen switched places. The eval increase showed that this was significant.


Stockfish continued to chase the black king, this time Leela started to lose material. The game was adjudicated with the white rook as the only piece left on the board. Stockfish wins the game pair and its lead increases to +4.

In game 69 Stockfish sacrificed a knight and bishop for 3 pawns, then moved its 3 heavy pieces to the open e file. Stockfish exchanged its rooks for the white queen on the back rank, the game reached a RRB vs Q position on move 31. Stockfish was 4 pawns up and evals were close to 0. Leela captured a few pawns while the black passers advanced, eventually Leela lost the bishop for a passer and the game was adjudicated. In game 70 Stockfish castled early and Leela pushed a pawn to h3. All pieces remained on the board until move 25 and evals were close to 0. Leela opened the queen side and created a passer, then started a series of exchanges with a knight sacrifice. On move 32 only RR vs RB remained, Stockfish had to be careful not to get mated in the corner and Leela used the time to exchange a pair of rooks and protect its passer with the bishop. The black king moved forward, Stockfish ended the game in a repetition draw to prevent a promotion.

Tuesday, June 30, 2020

Season 18 superfinal games 51-60

After 60 games Stockfish leads 14-9 with 37 draws. Stockfish wons 3 game pairs, increasing its lead significantly. Leela should have won a game pair but it blundered into a very deep winning line that only Stockfish saw.

Stockfish moved its king without castling early in game 51. Leela was a pawn down but had an eval advantage, the black king side rook was trapped in the corner. The engines exchanged minor pieces and Leela regained the pawn. Stockfish released its trapped rook, the game reached a QRB vs QRB position on move 30, Leela had a queen side passer. After exchanging queens Stockfish used its pieces to prevent the passer from advancing After some shuffling the engines exchanged rooks and reached an opposite color bishop ending. Leela was two pawns up but it was still a draw, the game was adjudicated on move 107.

Leela did not castle its king in game 52, the black pieces were mostly on the back rank and the engines played on the queen side. The b file was half open and Stockfish placed a rook there, its eval started to increase when it added a second rook and threatened the black b6 pawn. Leela couldn't defend the pawn, its eval was still relatively low.


After Stockfish captured the b6 pawn the engines exchanged most pieces. Leela soon realized it was in trouble, in a RB vs RB position its rook was still trapped on the king side. By the time the rook broke out it was still on the wrong side of the board. Stockfish gave its bishop and pushed a pawn to the 7th rank, Leela lost its rook to stop it. 


The rook was much stronger in this position, Leela tried to protect its a pawn but Stockfish just traded the rook for the bishop. The white a pawn became a passer and raced forward, promoting first for the win. Stockfish wins a game pair, its lead is now +3.

Games 53-54 started with a 23-ply book, a popular line in the King's Indian, Orthodox variation. Leela pushed a pawn to a6 in game 53, Stockfish pushed pawns on the king side. The engines exchanged all bishops, then Leela's queen moved deep into black territory. Leela captured a pawn but it could not retreat. Stockfish gave a series of queen "checks", Leela's eval came down and the game was adjudicated. In game 54 the setup was similar. Stockfish's eval went over 1 for a while after it opened the queen side and went a pawn up. Leela regained the pawn, evals came down and the engines exchanged bishops and a pair of rooks. The game ended in a 3-fold repetition.

In game 55 the engines castled in opposite directions. Starting from move 10 there was a series of moves following long agreements in the engines' PVs. Most pieces were exchanged and the game reached a RB vs RB position with white a pawn up on move 22. Evals slowly increased, Stockfish moved its king to protect the queen side pawns, its pieces stayed on the king side where Leela had a pawn majority. The engines exchanged rooks, leaving a same color bishop ending. Stockfish's eval was over 4 for a few moves, Leela couldn't find the win and evals came down. The rest of the game was a long shuffle with a few pawns moves and exchanges. The game was adjudicated on move 191.

The engines castled in opposite directions again in game 56. Again there was a series of exchanges with long PV agreements. On move 22 only RRN vs RRB remained, and Stockfish went a pawn up.


Stockfish exchanged a pair of rooks and its eval jumped over 2. The engines traded pawns and Stockfish's eval continued to increase quickly, Leela's eval also started to increase. Stockfish managed to capture all the black pawns and it had two pawns left, one on each side.


The game continued for another 30 moves. Leela delayed the advancing white pawns as much as it could, Stockfish pushed one forward and then the other. Eventually Stockfish found a way to capture the bishop and the game was adjudicated. Stockfish wins the game pair and the lead increases to +4.

Stockfish castled long in game 57, Leela did not castle at all. There were no pawn exchanges after the start, Stockfish's eval came down to 0 and stayed there for the rest of the game. The engines opened a file on the king side and after some shuffling exchanged a pair of rooks. There was a long shuffle starting from move 32, with one pawn move. A few exchanges led to a QRN vs QRB position, then shuffling resumed. Leela lowered its eval for the draw rule on move 126.

The kings' setup was different in game 58, Stockfish as white castled long and Leela castled short. Leela pushed pawns on the queen side while Stockfish gave a pawn and opened a file on the king side, both evals came down. Leela started to plan how to get its king out of the exposed king side, meanwhile it moved its queen to protect a pawn and Stockfish thought that Leela chose the wrong square. It gave a second pawn and opened the center, its eval jumping to around 2.


The black king was out in the open and Stockfish chased it all the way to the b5 square. Leela predicted all these moves in advance yet its eval stayed low. Stockfish had to be careful not to get mated on the back rank, the attack ended with a series of exchanges that left a Q vs RR position.


It took Leela a while to see it was losing. Stockfish pushed the f pawn forward and captured the remaining black pawns. Leela's king was pushed back and Stockfish pushed a second pawn forward before the game was adjudicated. Stockfish wins another game pair, the lead is now +5.

In game 59 Leela appeared to sacrifice its queen for a knight almost immediately at the start. In fact this was the beginning of a combination that included taking the black queen with a pawn. On move 11 Leela was a pawn up with evals over 1.


Leela sent its king to the queen side and developed its queen side pieces. Stockfish gave a pawn to break up the white queen side pawns, its king moved to the king side where there was only one pawn left. The game reached a RRN vs RRN position, Stockfish got one pawn back while evals continued to increase. The engines traded a pair of rooks, all the black pawns were isolated and Stockfish tried to keep them alive.


The white rook moved forward and Stockfish couldn't stop it from taking the queen side pawns. Leela was 3 pawns up with connected passers and the game was adjudicated.

Game 60 started much more quietly. Leela castled its king, Stockfish decided not to since both sides were too exposed. Leela opened a file on the queen side, exchanged a pair of rooks and went a pawn up. Evals remained low, the engines traded R for BN and the black queen moved forward. On move 32 Leela moved its queen, immediately Stockfish's eval jumped to 24 (!!). Leela's eval predicted the next 7 moves correctly, but its eval remained low. Stockfish sacrificed a bishop and exposed the black king.


Stockfish presented 100% tablebase win scores, Leela remained confident it could hold despite the white queen being so close to its king. Stockfish exchanged bishops and moved the passer to e7, Leela had to block with a rook. Stockfish was careful not to allow a perpetual check threat, the knight came forward to protect the passer and threaten mate. Leela soon ran out of checks, its eval was over 2 and it again dropped, really having trouble in understanding the position.


Stockfish captured a pawn and exchanged queens, Leela tried to race to the line but Stockfish threatened mate in the corner, captured the rook and promoted first with check. There were two white wins in this opening, though Leela should have held the reverse. Stockfish's lead remains +5.

Sunday, June 28, 2020

Season 18 superfinal games 41-50

After 50 games Stockfish leads 10-8 with 32 draws. Leela got within 1 point twice, and Stockfish won the reverse game in both game pairs. At the halfway point of the match Stockfish keeps a 2 point lead, still quite close and anything can happen. 

Games 41-42 started with a Scotch game modern defense variant, the black queen came forward and the black king moved and could not castle. In game 41 there were many early exchanges and only QRB vs QRB remained on move 18.


Evals slowly increased, Leela was a pawn down but had a better pawn structure, especially on the king side where Stockfish had doubled pawns. The engines exchanged queens and Leela managed to capture all the black pawns on the king side. 


Leela was careful and patient with its king side pawns, after 15 moves Stockfish decided to give its bishop and remove them. Leela had enough pawns left to win a RB vs R ending.

The pieces stayed on the board a bit longer in game 42. After exchanging queens Stockfish had a bishop pair, Leela went a pawn up but Stockfish's eval started to increase. Stockfish traded a bishop for a knight and only RRB vs RRN remained on move 27, Stockfish's eval was over 2.


Stockfish captured a pawn on the king side and created a 3 to 1 pawn majority. The engines exchanged pawns and Leela created 2 passers on the queen side. It pushed a pawn to the 2nd rank and its low eval showed it thought it was relatively safe. Stockfish's eval continued to increase, it controlled the 7th rank with a rook and it was sure it was going to win.


Leela couldn't hold on to the d pawn after the white king moved towards it. The other black passer was too far to be a serious threat, Stockfish doubled rooks on the 7th rank and Leela realized it was going to lose.


Leela avoided an immediate mate but Stockfish captured the knight a few moves later. The game was adjudicated in a RB vs R position with one white pawn to ensure the win. There were two white wins in this opening, lead is still +2.

Game 43 reached a R vs NN imbalance early. Leela was two pawns up, the engines exchanged queens and a pair of rooks and the game reached a RB vs BBN position on move 32. Stockfish's eval came down to 0, the most Leela could do was to give a pawn a get a passer to the 7th rank. Leela continued to play, the game was adjudicated in a R vs BN position on move 78. In game 44 Leela pushed pawns in the center and planted a knight on the 3rd rank. Stockfish exchanged a bishop for the knight and cleared the black central pawns. After a series of exchanges the game reached a RN vs RN position on move 35. Both engines had a pawn near promotion, after a while they traded knights and captured the passers leading to a drawn rook ending. 

In game 45 Leela pushed pawns in the center and Stockfish pushed pawns on the queen side. Evals mostly stayed below 1, Leela waited until move 20 to castle though its king had low pawn cover. Leela surprised Stockfish on move 23 with a pawn move to f5. The white king side completely opened, and then Leela gave a pawn and created an advanced passer in the center. Stockfish's eval jumped over 2, a series of exchanges led to a RBN vs RBN position.


The black knight was almost trapped, Stockfish lost two pawns to save it. While Stockfish concentrated on getting rid of the passer Leela captured another pawn, it was two pawns up in a RN vs RB position on move 49.


Leela drove the black king back and captured another pawn, the game was adjudicated soon after that.

In game 46 Stockfish pushed pawns on the king side and castled short like the previous game. There were several early minor piece exchanges and queens were also off the board. Stockfish's eval started to increase after Leela grabbed a pawn on the queen side and allowed Stockfish to create a pawn majority on the king side. The white king moved forward supporting its pawns and Stockfish placed a bishop and pawn pair deep in black territory. After exchanging a pair of rooks the game reached a RBN vs RBB position and Stockfish went two pawns up.


The black bishop pair was strong, Stockfish's passer could not advance and it was not clear how Stockfish can win, though its eval continued to increase. On move 50 Stockfish traded its knight for a black bishop, then traded rooks and gave its passer to take the black h pawn.


The result was an opposite color bishop ending. Usually a 2 pawn advantage is not sufficient in such an position but this was an exception. The connected pawns needed the attention of both black king and bishop, and by the time Leela captured one pawn Stockfish pushed the c pawn to the 6th rank. Leela could not stop both white passers and Stockfish promoted one to a queen, winning the game. There were two white wins in this opening, lead is still +2.

Leela opened the king side and castled long in game 47. Stockfish exchanged queens and opened the queen side, its eval dropping to 0 though Leela was a pawn up. Only rooks and bishops remained on move 29, both kings were exposed to checks. Leela avoided a repetition draw but the draw rule adjudicated the game. Game 48 started with a similar setup with Stockfish castling long. The white queen came forward and Stockfish tried a king side attack. Leela defended well, it tried to exchange queens but Stockfish refused. After several attempts there was a series of exchanges instead and the game reached a QN vs QB position on move 35. Evals were low, the game continued for 35 moves and was adjudicated when the pawns stopped moving.

Black had an advantage from the opening in games 49-50. In game 49 all the bishops were exchanged by move 16, with all pawns still on the board. Leela didn't castle its king, instead the king walked to the king side. Stockfish's eval came down and it mostly played waiting moves. The engines opened a file on the queen side and exchanged a pair of rooks, after that the game was adjudicated by the draw rule. In game 50 Stockfish castled early and the engines exchanged pawns with all pieces on the board. Leela didn't castle as black, starting from move 21 the engines exchanged pieces and on move 29 only RB vs RB were left with Stockfish a pawn up. The engines mostly shuffled with some pawn moves or captures, Leela slowly lowered its eval. The game was finally adjudicated on move 103, close to a 50 move draw. 

Saturday, June 27, 2020

Season 18 superfinal games 31-40

After 40 games Stockfish leads 8-6 with 26 draws. Only one decisive game, Leela wins a game pair and Stockfish's lead is +2. The match is not so one-sided as it was in the first 10 games, Leela is still fighting.

A long series of early exchanges left only RRB vs RRB on move 21 in game 31. The engines stabilized the pawns and then exchanged a pair of rooks. A second series of exchanges reduced to an opposite color bishop ending, Leela had connected passers and Stockfish had a passer that reached the 2nd rank. Leela thought it had an advantage, it took a long time for it to lower its eval for the draw rule on move 96. The pieces stayed on the board longer in game 32, the engines cleared the queen side pawns and exchanged queens and minor pieces. Evals came down to 0 and the game was adjudicated when the pawns stopped moving.

The center opened early in game 33 and the engines exchanged most pieces. Evals climbed over 1.5, on move 25 only BB vs R remained. Stockfish was a pawn up but it had two weak pawns on the queen side and only one piece to defend them. 


The bishop pair was very strong, Stockfish played passively and tried to protect its pawns. Leela's king came forward targeting the black a pawn. There was no room for the rook and king as defenders and Stockfish lost the a pawn on move 46.


The black rook became active again, but it couldn't attack on its own and the white pawns were protected. Leela slowly pushed the a pawn forward, with its king and bishops supporting. The game was adjudicated when the white king found a way to move behind the black pawns.

In game 34 the black queen came forward early, Leela traded it for two bishops and a knight. Stockfish captured two pawns and its eval went over 2 and kept increasing. Both engines attacked and the position became chaotic, Stockfish threatened mate on the king side while Leela pushed two pawns on the queen side facing the white king. After material sacrifices from both engines the game settled down in a Q vs RN endgame on move 39. 


Despite the high eval Stockfish could not find a way to win here. Leela abandoned the a pawn and placed its rook on the 6th rank. Together the rook and knight controlled the d6 square, stopping the white pawn. Stockfish got nowhere with its queen alone and it gave up trying as the 50 move draw approached. Leela wins a game pair and Stockfish's lead is +2.

Leela pushed pawns on the queen side in game 35, despite castling long. A file opened in the center and the engines exchanged queens and a pair of bishops. Evals were low and the engines started to shuffle. There were a few more piece exchanges and pawn moves, the game was adjudicated when Leela lowered its eval for the draw rule. In game 36 Stockfish castled short and Leela pushed a pawn to h3. Stockfish went a pawn up, its eval peaked at 1.5 and then came back down. The engines cleared most of the pawns on the queen side, then shuffled for a while. Evals were close to 0 and the game was adjudicated on move 35, in a position with many pieces and pawns on the board. Too soon?

Leela pushed a pawn to h6 in game 37, and Stockfish castled short nevertheless. The engines exchanged queens and all bishops, that made the black king safe. After exchanging a pair of pawns the engines started to shuffle on move 35. Evals were around 1 but neither engine moved a pawn and the game ended in a 50-move draw. Game 38 started similarly with a white pawn on h6 and Leela castling short. Stockfish attacked the king side, capturing two pawns and making its h pawn a passer. Leela hid its king behind the passer and exchanged queens. Leela avoided opening a file on the king side and exchanged bishops, its king was trapped in the corner but somehow safe. Evals came down and the game was adjudicated in a RRN vs RRN position, Leela's PV showed a drawn double rook ending.

In game 39 Leela pushed pawns on the king side and its king stayed uncastled in the center. Stockfish opened a file on the king side and gave a rook for a bishop. The white king was exposed and Leela quickly exchanged queens, Stockfish's eval came down to 0. The game reached a RRN vs RBN position, and the engines gradually exchanged pawns until none were left. The material advantage was not enough for a win, Leela was slow to lower its eval and the game was adjudicated on move 90. In game 40 again Stockfish pushed pawns on the king side, it did castle its king but without pawns the king was still exposed. Leela gave two pawns and opened a file in the center, its eval turned negative after it doubled rooks in the file. Leela went on the attack with many threats and pins, however Stockfish's eval was at 0. After most pieces were exchanged the game reached a RB vs Q position with white two pawns up. Leela could only give checks, after 25 moves it lowered its eval for the draw rule.

Friday, June 26, 2020

Season 18 superfinal games 21-30

After 30 games Stockfish leads 8-5 with 17 draws. Both engines won a game pair, first game pair win for Leela. Stockfish continues to lead by 3 points.

Stockfish gave a pawn early in game 21, then the engines reduced to a RB vs RB position on move 21. Leela created a queen side passer and Stockfish blocked it with its pieces. The white king could not move forward and the engines shuffled for a long time. Stockfish ended the game with a perpetual check. In game 22 all the pieces were on the board on move 25 except for one white pawn and a pair of bishops. The white queen went forward and captured two pawns, Leela opened the king side with a rook sacrifice and attacked the white king. A long series of exchanges led to a N vs BN position with white two pawns up and low evals. The game continued for 60 more moves with pawn moves and exchanges before it was adjudicated.

Games 23-24 started with a 20-ply book in the Queen's indian, Petrosian variation, with black a pawn up.
In game 23 evals increased slowly after the start, and most minor pieces were exchanged. Leela opened a file on the queen side and doubled its rooks there. Evals peaked at around 1.5, then the pawns stabilized and the engines started to shuffle. After 35 moves a pair of rooks was exchanged and then queens as well. The engines continued to shuffle in a RN vs RB position, evals slowly came down. The rooks were eventually exchanged as well, the game was adjudicated on move 175.

There were less exchanges after the start of game 24, Stockfish's eval stayed around 1. The black pieces were pushed back and Stockfish had more space, but it didn't seem to have a clear plan. After move 30 Leela played a few moves that were inaccurate according to Stockfish, on move 35 Stockfish's eval jumped over 3.


The white queen had a diagonal line of sight to the black king, Stockfish used the check to move the queen forward on the queen side, and a rook followed in the center. The attack on the black king included a temporary rook sacrifice, the attack was over in a QN vs RRB position on move 48. The material was close to equal yet Stockfish's eval was close to 10. Leela's eval was much lower, still hopeful.


The queen danced across the board, giving checks and preventing any counter Leela might try. After 20 moves Stockfish captured a rook and the game was adjudicated. Stockfish wins the game pair, its lead increases to +4.

Stockfish was a pawn up early in game 25, evals were low around 0.5. Stockfish moved its king side rook and decided not to castle its king at all. Evals increased slowly as Leela increased the pressure on the king side. It pushed a pawn to h6 and threatened mate, Stockfish saved its king but its king side rook was trapped in the corner.


Leela traded its bishop for the rook, and the black queen got trapped in the corner. Leela's queen came forward and captured two pawns before Stockfish could untangle itself.


The game continued for a few more moves, but the material advantage gave Leela the win.

As before Leela was a pawn up in game 26. This time Leela chose to castle long despite the partial pawn cover on the queen side, and its king side rook was free to move. Stockfish's eval was around 1 as it slowly moved pieces to the queen side. Leela doubled rooks on the g file and created pressure on the g2 pawn and the white king. Stockfish had to defend carefully, its position seemed very hard to hold, yet its eval went over 2.


Leela saw its attack wasn't going anywhere but it was difficult to retreat, it tried to exchange queens but Stockfish refused. Stockfish opened another file on the queen side and its two rooks trapped the black king, preparing for the final attack.


Stockfish traded a rook for the defending knight, the white queen left the g2 pawn and went on the atttack. Leela was forced to give its queen for a rook to avoid immediate mate, but it couldn't save the game. The white knight joined the attack and Stockfish won more material to win. Two white wins in this game pair, no change in the lead.

Games 27-28 started with black a pawn up. Stockfish's eval started at (negative) 1 in game 27, then came down after the engines exchanged a few minor pieces. After exchanging queens Leela had a bishop pair to compensate for the pawn. Evals were close to 0 after move 20, the engines continued to exchange pieces and Leela regained the pawn. In a king and pawns ending both engines promoted a pawn to a queen, the game ended in perpetual check. In game 28 Stockfish's eval again reached (negative) 1, then came down when the engines started a series of exchanges. By move 33 the game reached a knight ending, with adjudication 10 moves later.

Leela pushed pawns on the queen side in game 29. The black pieces were pushed back, Leela opened a file and one of the pawns reached a6. Evals slowly increased as the engines exchanged pieces and pawns, Stockfish couldn't get rid of the white a pawn. On move 31 the game reached a RB vs RN position.


Stockfish could have taken the a pawn but chose not to do it since that would bring the white rook to the 7th rank. Instead Stockfish exchanged the minor pieces and reduced to a rook ending, its eval jumping as it realized it was losing. The kings moved forward and the pawns stabilized, Stockfish found itself in near zugzwang. Leela pushed a pawn to g6, creating a second entry point to the 7th rank for its rook. Leela's eval went over 2.


The white king moved to the queen side and threatened to penetrate. Stockfish had to move its rook to stop the king, allowing Leela to capture the e pawn. Leela took over the 7th rank, another black pawn was captured and the game was adjudicated.

In game 30 Stockfish went a pawn up tried to attack on the king side but was not strong enough. The engines exchanged pieces, Leela regained the pawn and evals came down to 0. The exchanges continued until the game reached a drawn rook ending. Leela wins a game pair for the first time in the match, the lead is back to +3.