Thursday, December 17, 2015

Season 6 superfinal, games 17-24

This is part 3 of my looking back at the TCEC season 6 superfinal match between Stockfish and Komodo. Previous parts can be found at

part 1, games 1-8
part 2, games 9-16

After 16 games Stockfish led by 3-0 with 13 draws.

Game 17 started with an eval advantage for Stockfish, but after some exchanges the engines started shuffling pieces with very few pawn moves that were available. After a while Komodo sacrificed two pawns which allowed it to attack white's king, eventually forcing a 3-fold repetition. In game 18 Stockfish quickly equalized as black by sacrificing a pawn and opening up the queen side against Komodo's king (long castled). The evals showed a growing advantage for Stockfish within a few moves.

With so much firepower aimed at Komodo's king, mating threats at move 17, Stockfish was clearly in charge. Komodo started to lose material, first a knight for pawns, and then a rook for a knight.

This was game over, though it continued a bit until both engines had a high enough (negative) eval. A very impressive win for Stockfish especially considering the previous game. It clearly analyzed the opening much better than Komodo, from both sides of the board.

In game 19 Stockfish had an eval advantage out of the opening due to a bishop pair compared to Komodo's pair of knights. A few moves later after a bishop and knight exchange, Stockfish was a pawn up but with two pairs of doubled pawns, while Komodo had control of the center with a connected pair of passed pawns. Stockfish gave a rook for a knight to break the black center but this only led to a drawn ending of bishop and pawns against a rook. In game 20 Komodo went for an imbalance of BB vs R, which Stockfish thought was in its favor with white underdeveloped and the white king vulnerable in the center. After the queens were exchanged Komodo's pieces found more space and it built a fortress in the center for its king.

Cute !! After a few more moves the game was settled with 3-fold repetition.

Game 21 featured a bishop sacrifice by Stockfish in an attempt to expose the black king to attack. There followed many trades and threats on both sides, and in the end this was only good for a perpetual check draw. In game 22 Stockfish attacked as black, sacrificing a knight to open the h file against Komodo's king. Later Stockfish tried to put as many pieces as possible on the file, but Komodo used this to find a perpetual check on the other side.

In game 23 Komodo started with a pawn advantage as black, but it chose to give two pawns back to gain a connected pair of passed pawns. Stockfish sacrificed a knight to get rid of these pawns, leading to a drawn endgame of RR vs RRN with both kings exposed to check threats. The game was adjudicated before the perpetual checks started. In game 24 Stockfish kept the pawn and attacked the white king. Komodo exchanged pieces and successfully defended its king. As in the previous game Stockfish obtained a connected pair of pawns but only for a short while. The exchanges continued until there were only QR vs QR with no way to make progress for either side.

The result after these 8 games was 4-0 for Stockfish, which seems to be dominating this match. Komodo has not been able to find a way to win yet while Stockfish is constantly attacking and looking for chances.

Thursday, December 10, 2015

Season 6 superfinal, games 9-16

Welcome to part 2 of my look-back at the Season 6 superfinal. In this part I cover games 9-16. After the first 8 games Stockfish was up by 2 wins, with 6 draws.

Link to part 1, games 1-8

Game 9

The opening had a small bias for white and Stockfish gradually increased the eval advantage. After 21 moves the material was balanced but Stockfish was threatening f7.

It looked as though Komodo had it covered but the two knights were quickly chased away. Stockfish then initiated a combination that resulted in a Q vs RR imbalance.

With black's king exposed in the center the white queen could attack quickly from both ends of the board. Gradually Stockish converted this advantage into material, first pawns, then a bishop for rook exchange, and the game ended after the second black rook was exchanged for a knight.

The reverse game was very different. Stockfish as black neutralized the king side quickly and castled, while Komodo castled long, and the action concentrated on the queen side. After queens were exchanged and the pawns stabilized both engines reached a 0 eval and the game was declared a draw. So, 3-0 Stockfish and 7 draws.

In game 11 Stockfish launched a strong king side attack, with eval rising above 0.9 (Komodo peaked at about 0.5). Komodo defended well, first stopping the attack and exchanging material, and then finding a perptual check for the draw. In the reverse game it was again Stockfish that had a slight advantage as black, but it was not enough for a win.

Game 13 reached a NN vs BN endgame on move 27, with the evals close to 0 throughout the game, resulting in a quick draw. The pieces stayed on longer in game 14 and Komodo had some hopes with a small eval advantage. After Komodo took over the 7th rank Stockfish responded by trading most pieces and securing a passed pawn. This threat forced Komodo to draw with perpetual check even though it was a pawn up.

In game 15 Stockfish had a small eval advantage for a while, but with only QRB vs QRN with many pawns left at move 23 the game looked to be heading for a quiet draw. For a short period Stockfish got excited with eval jumping to 0.5 and even 0.9 for one move, but Komodo remained cool and defended against any pawn breaks or king attacks. When the queens were exchanged the evals dropped to 0, and while Stockfish had a passed pawn on the 7th rank Komodo ended the game by check repetition. Game 16 developed along similar lines with the same piece composition for the endgame. Here there were no attempts to break the pawn lines and the game ended quickly in a shuffle with 0 evals.

Tuesday, December 8, 2015

Season 8 superfinal, games 91-100

Finally season 8 has come to an end. The final result of the Komodo-Stockfish match is a win for Komodo, 9-2 with 89 draws. No real surprises here, we've seen this win for Komodo coming for a long time. It even grabbed another win in the last 10 games to increase the lead. The engines and their programmers can take a well deserved break, and then start preparing for season 9 - even better hardware and better engines, fewer bugs and more exciting games.

Game 91 reached a RB vs RB endgame by move 27, with Komodo a pawn up but with doubled pawns. The evals quickly dropped to 0 and the bishops and pawns were gradually exchanged. The game ended in a 6-man tablebase draw where Komodo had a two pawn advantage, the f+h rook endgame - easy if you have access to 6-man tablebases. Game 92 was very short, a 3-fold repetition on move 26 with a lot of pieces still in play.

Game 93 started with an eval advantage of over 0.6 for Komodo and a pawn advantage as well. The evals jumped up to over 1.2 when Stockfish was tempted to take a pawn, and Komodo gave a rook for a bishop to gain a passed pawn and a strong pair of bishops. Komodo fans started to fantasize about another win but Stockfish patiently defended, blocking the center with a knight, giving back the exchange and trading rooks. Komodo remained optimistic for a while longer but in the end the kings were too exposed and the game ended with perpetual check. In game 94 Stockfish could not hold on to the initial eval advantage and by move 34 the only pieces left were the queens. It took a while for the game to be adjudicated because of all the pawn moves and captures, but the draw was inevitable.

In game 95 Komodo had a small advantage after the opening even though Stockfish was a pawn up. Black's position was very cramped and less developed than white at first, but after a while the position opened a little and it seemed Stockfish could hold out. Komodo's eval started to rise again to over 1, causing more anxiety for Stockfish fans. At one point Komodo regained the pawn and had a dangerous passed pawn, but after queens were exchanged the position stabilized at a RB vs RB ending with opposite color bishops and Komodo a pawn ahead. It took a lot more moves for both engines to see that the position was drawn. In game 96 Stockfish regained the pawn very quickly, and there were many exchanges in the opening. The game reached a BBN vs BBN position on move 23, and the evals dropped after knights were exchanged. Stockfish kept a small eval that let the game continue for a long bishop shuffle before agreeing to a draw.

Game 97 was more or less balanced with a small eval advantage for Komodo. Stockfish seemed to be defending well until move 30.

For no apparent reason Stockfish weakened its king position by moving the f pawn forward. The evals started to jump immediately and within a few moves the h file was open for attacking the king.

Stockfish position deteriorated very fast. After the queens and a few pawns were eliminated the game was stopped with another Komodo win.

Komodo is only a pawn ahead but the b pawn is unstoppable with too many black pieces stuck on the king side. Another case of Stockfish not playing well in a closed position. 9-2 Komodo, not even a miracle can change the result now. In game 98 pawn lines were formed very quickly and both engines started to shuffle pieces at move 16. From move 38 the pawns became static and the game continued until nearly the 50 move rule, when Stockfish lowered its eval enough for the game to be stopped.

In Game 99 Komodo had an eval advantage of about 0.5 with many exchanges after the opening. Stockfish sacrificed a knight for two pawns, this time as a defense and not an attacking move. Pieces were gradually exchanged and the position simplified to a RBN vs RB ending. After the bishops and all white pawns were gone the RN vs R game was theoretically drawn, it just took a while to get there.Game 100, the last game, everyone was tired and wanted to go home, including the engines. Stockfish had an eval advantage for a while, but the pawn structure became static on move 26 and then the evals reached 0. The game was adjudicated as fast as the TCEC rules allowed.

Saturday, December 5, 2015

Season 8 superfinal, games 81-90

After 90 games in the Komodo-Stockfish superfinal match, Komodo is leading 8-2 with 80 draws. With 10 games left there is no question which engine is going to win. Cato's openings are now 5/24 decisive, quite a change comparing to the first 5/66 decisive games. Stockfish has managed to win a second time, a small consolation for all the games Komodo has shown its superioirity.

In game 81 there were many exchanges in the opening stage and by move 30 the queen side was cleared and the pieces left were RB vs RN. Komodo was a pawn up but there wasn't enough material to increase the advantage. The game was adjudicated shortly after the rooks were exchanged. In game 82 many pieces were exchanged as well. Stockfish sacrificed a bishop for two pawns to get a pair of connected passers, but Komodo responded by giving back the material to stop the pawns from marching.This led to a drawn RN vs RN ending.

In game 83 there was some drama not directly related to chess. It started with an eval advantage for Komodo which gradually grew. It got to a point where the trend was clear and both engines seemed to agree that Komodo is going to win. I had something to do and did not watch for a couple of hours, but when I came back the game was still going on, or rather it was replayed. Later I understood from the chat that the server crashed in a clearly winning position for Komodo. There were some angry Komodo fans, but the protest wasn't so loud because Komodo was leading 6-1 at this point - if it were Stockfish the noise would still be heard.
When game 83 was replayed Komodo again started with an eval advantage that grew to over 1. Komodo won a pawn in a complicated position.

The evals stayed about the same for the next 15 moves while there were many exchanges on the board. It was not clear if a single pawn would be sufficient for a win with this pawn structure and the remaining pieces.

After the rooks were exchanged the black DSB was very weak and the LSB could not afford to be exchanged, allowing Komodo to gain another pawn.

Now the game was over, Stockfish could not defend against the king side pawns without losing more on the queen side. So in the end Komodo won in the rematch and the server crash did not change the result. For game 84 Stockfish fans hoped that if Komodo could win twice in a row as white then perhaps Stockfish could as well.However, with Stockfish as white the evals went down very quickly and material was equal. Each engine had a passed pawn but neither was able to get an advantage in the game. When both sides started to shuffle the game was adjudicated. Komodo was at 7-1, a bit embarassing for Stockfish.

In game 85 the board was cleared very quickly leaving a lot of space for the heavy pieces, especially on the queen side where there was only one pawn left by move 22. On move 38 an endgame of RPP vs RP was reached which was theoretically drawn. Komodo kept an eval over 0.6 which meant the game would be played on for a long while. It took another 60 moves before the game was stopped. Game 86 started on a different path, with pawns blocking the center and pieces shuffling behind. There were opportunities for flank attacks but with equal material and both evals at 0 it seemed like a potential quick draw.

Then out of nowhere the evals became negative at about -0.9, Komodo was pressing on the king side and Stockfish defending. Another case of "shuffle to Komodo win" for this match? But where was the win coming from? Knights were exchanged and with so many pawns the heavy pieces had a hard time moving. Komodo was able to infiltrate white's ranks and to get a pawn advantage, but there was a long sequence of shuffling moves with no eval change, perhaps Stockfish is holding? After queens were exchanged Komodo started to improve its eval.

One pair of rooks was exchanged and the black king attacked the central white pawns. Stockfish's only asset was the passed a pawn but it was not enough.

There was no way for Stockfish to keep the a pawn or to defend against all of Komodo's pawns advancing. 8-1 for Komodo, unbelievable, inconceivable (as Inigo would say...).

Game 87 was very quiet, reaching a BNN vs BNN endgame on move 29. The pawns and pieces were gradually exchanged and the game reached a tablebase draw. In game 88 Stockfish started with a small eval advantage, but around move 20 it started to jump up to a level of 1.5, while Komodo remained skeptic. And then came the knight sacrifice.

We haven't seen such a move from Stockfish in a long time. Right away Komodo saw it was in trouble, with too many pieces on the queen side and a vulnerable king side. There came a beautiful series of moves, Stockfish opened the king side and forced a series of exchanges that left it two pawns ahead.

The game wasn't formally over for another 25 moves but there was no doubt that Stockfish would win, two pawns in the endgame is just too much at this level of play. This was a totally unexpected win for Stockfish. Not that 8-2 is a lot better than 8-1, but this is the style we love to see in Stockfish games, and Komodo doesn't usually allow this to happen.
Game 89 reached an RB vs RN endgame by move 28. Komodo's small eval advantage was gone after the rooks were exchanged, and the game turned into a queening race. Both engines queened a pawn which eventually led to a tablebase draw. Game 90 reached a RRN vs RRN position in move 24. Stockfish had a pawn advantage but weak pawn structure with two pairs of doubled pawns. Stockfish rooks were more active and the eval increased to 0.6. Komodo defended well and the evals remained constant until dropping to zero as the game winded down to another tablebase draw.

Tuesday, December 1, 2015

Season 8 superfinal, games 71-80

After 80 games in the Komodo-Stockfish superfinal match, Komodo is leading 6-1 with 73 draws. In the last 10 games Komodo has struck twice, both wins in black, both started with white having an advantage. With only 20 games left is seems almost certain that Komodo will win the match. The two wins by Komodo also show that it is better than Stockfish in getting out of long shuffles with a winning position.

With two decisive games and several exciting draws, Cato's opening choices are doing well.

Game 71 started with a small eval advantage for Komodo, which then decreased gradually to 0 when there were only RRN vs RRN left. Stockfish had a passed pawn that wasn't going anywhere but may be the reason Stockfish gave a negative eval at this stage. There came a long period of shuffling that got close to the 50-move mark, and after a Komodo pawn move there came a gradual removal of all pieces. The game stopped at a drawn RN vs R tablebase position. Game 72 started similarly with a small eval advantage for Stockfish. Starting from move 20 the engines shuffled for 25 moves, while all pieces were still on the board.

Here Stockfish pushed the b pawn with Komodo countering with the f pawn, a few moves later the board was less crowded.

Stockfish's king looked a little vulnerable, and the evals favored Komodo - why stop shuffling if this is the result? Komodo put its knight on f3 making life harder for the white king and gradually increasing the eval. After queens were exchanged Komodo put a rook on the second rank and the pressure on the white king increased.

Could Stockfish hold this position? After a rook exchange Komodo used a threat on the h pawn and its passed e pawn to force Stockfish to lose the bishop for a pawn.

Stockfish was lost here, both engines saw that the white pawns were soon to be captured and the last black pawn couldn't be stopped. Stockfish lost the game just because it wouldn't continue the shuflling, and Komodo saw how it could turn the game around better than Stockfish. Well done Komodo, Stockfish needs to improve its skills.

Game 73 was a bit wild, with exposed kings and advancing passed pawns for both engines. Komodo started with an eval advantage, but as the game progressed and the threats became evident the evals went closer to 0, and then Komodo went for a RNP vs Q trade. What could have been an interesting imbalance turned into a perpetual check draw in a few moves. Game 74 started with a rook for bishop exchange by Komodo, followed by a queen exchange, but then the action stopped. By move 22 the game reached a RRB vs RBB endgame, and gradually the pawn structure made it difficult for the pieces to move and a draw was adjudicated.

In game 75 the evals went down to 0 in a quiet game, and then when the draw was sure the action started. A rook for bishop exchange, a rook and queen sacrifice followed by a queening and regaining the rook, and finally another  rook sacrifice and a perpetual check. A roller coaster draw. In game 76 Stockfish was able to keep an eval advantage of about 0.7 well into the game, reaching a RB vs RN endgame by move 30 with a pawn advantage. That's as far as it got for Stockfish, Komodo patiently exchanged pawns and the evals kept going down until they reached 0 again.

In game 77 all the queen side pawns were taken by move 21, and by move 31 the only pieces left were B vs N. The game continued until a tablebase draw, at least the game was relatively short.In game 78 most of the pawns remained on the board with the heavy pieces in a standoff behind them.

Stockfish started seeing repetitions in the PV while Komodo saw a small advantage in eval, two warning signs for Stockfish fans. Stockfish put all possible pressure on the c6 pawn, neglecting the king side.

Komodo very quickly took advantage, breaking the pawn structure on the king side and trapping the white king.

By the time Stockfish could untangle its pieces it was too late. It was an exchange down, the king trapped and with too many pawns to defend.

The game was adjudicated but the PV shows that once queens are exchanged there is nothing to stop the rook from attacking the pawns from behind, the bishop cannot defend them all and the king is too far away. So, another win for Komodo, again showing it gets out of pawn blockades better that Stockfish. Is Komodo just seeing farther than Stockfish? Is this the result of a bug?

Games 79 and 80 started with a pawn advantage for white out of the opening. In game 79 after many captures by move 24 all queen side pawns were gone except for a passed pawn for Komodo, and a few moves later the remaining pieces were BN vs BN with opposite colored bishops. Komodo kept an eval advantage for many more moves but could not advance the passed pawn or make any progress on the king side. After a few more exchanges the game was finally adjudicated on move 113. In game 80 Stockfish kept a pawn advantage on the queen side but quite unexpectedly gave a rook for a knight. The white pieces were much more active than the black pieces as compensation, and Stockfish managed to capture a second pawn. In the RN vs RR endgame Komodo blocked the white pawns advancing and finally gave the exchange back to get a pawn back. Material equality was reached after the remaining rooks were exchanged and though both sides queened a pawn no side had an advantage.

Season 8 superfinal stats

Draw rate, wins

Final draw rate was 89%, very high but perhaps expected since it is very hard to beat these engines starting from a close to balanced position. The openings Cato chose in games 67-100 were slightly more unbalanced, and their draw rate was only 82.4%.

Moves per game


Games were much shorter than I expected. The draws tended to be short where both engines had 0 eval and the TCEC adjudication stopped the game. The median number of moves in the decisive games was 74.5.

Time per game (hours)


My prediction for time per game in the superfinal was off by 45 minutes... The short draws were something I didn't think would happen. In the end the games of the superfinal were similar in duration to the games of stage 3, even though each engine had 30 more minutes.


The first letter of the ECO codes of the superfinal openings was distributed as follows:

More or less even, biased for irregular openings and against open games and Sicillians.

If we use the opening 'family name' (using format FAMILY_NAME: VARIANT....) the top 3 are:

English - 16 times
Sicillian - 12 times
QGD - 8 times

Reverse pairs, wins

As much as Cato tried to choose biased openings, the engines still found ways to draw. Still, excellent choices by Cato since there were no biased 1-1 results.

Reverse pairs, same moves

How many plys did the engines play after book until the first divergence in the reverse games? 

Divergence was usually within the first move (2 plies). This shows that Cato chose openings that didn't have forced continuations so that each engine could try its own strategy. The longest the two engines agreed was 13 plys in games 47-48.

Friday, November 27, 2015

Season 8 superfinal, games 61-70

After 70 games in the Komodo-Stockfish superfinal match, Komodo is leading 4-1 with 65 draws. The last 10 games have all been draws, again. An important change is that from game 67 the openings are supposed to be more unbalanced, as preselected by Cato to try to lower the draw rate. The evals out of the openings are higher than before, but the first 4 games 67-70 were still draws. Still 30 games to go so we will have to wait and see.

Game 61 was very short. Stockfish went for the b pawn with the queen, and Komodo almost trapped it, leading to a draw by repetition. Game 62 started with many captures, reaching an RN vs RN ending in move 28 with Stockfish a pawn up. Both engines continued with 0 evals and eventually the game was adjudicated even though both had dangerous passed pawns. There was a possible repetition in the end but it wasn't played out... a draw in any case.

In game 63 Komodo started with a small eval advantage, but it disappeared when almost all the queen side pawns were captured and the pieces left were QRN vs QRB. Then Komodo's eval went up again as it got into the black back rank, but once the queens were exchanged Stockfish secured a king side fortress. It took many shuffling moves for Komodo to realize there was nothing to do, finally it broke the pawn structure to get out of the 50 move draw. This only led to a repetition draw later. In game 64 Stockfish held on to an eval advantage with an advancing passed pawn. All pieces focused on attacking and defending this pawn until the position was stuck, the engines chose to end with a repetition of checks.

Game 65 reached a RB vs RB ending by move 22, and then continued for more than 100 shuffling moves with a few pawn moves to reset the 50 move rule. Komodo insisted it had a small advantage, and the game could not be adjudicated until it realized what everyone knew for so long - it was a draw... Game 66 was played in a different line but just as drawish. This time the game reached a B vs N at move 30 and both engines had a 0 eval, allowing the game to stop without a long wait.

Game 67 was the first of the 'Cato openings' of the superfinal. There was a lot of hope that the games would be more decisive the way these openings were chosen. The first 4 were draws but there were higher evals in these games, so there is still hope.

Komodo started with an eval advantage that got up to 0.63 in game 67. Stockfish defended well and after 26 moves the pieces left were QRB vs QRB, Komodo a pawn up, passed and isolated. After the queens were exchanged and the pawns were taken one by one the evals dropped to zero. The game reached a 6-man drawn position. In game 68 Stockfish held its advantage longer and gave an eval of 0.9 for the isolated passed pawn it had, also a pawn up. Komodo defended well and Stockfish couldn't convert a win, gradually the pieces were captured until there was a rook ending. Stockfish was still a pawn up but not enough for a win.

In game 69 Komodo again had an eval advantage that got up to 0.7. Material remained equal but Komodo created a passed pawn after the queens were exchanged. Pieces kept being captured until there were only B vs N. It then took a while for both engines to lower their evals to agree on a draw. Stockfish didn't get as much out of the opening in game 70. As the game progressed Komodo was attacking on the king side and Stockfish countering on the queen side. Both engines started to see perpetual check in the future but Stockfish went for a bishop and pawns for rook exchange, forcing the draw when Komodo was left with KR with no pawns.

Wednesday, November 25, 2015

Season 8 superfinal, games 51-60

After 60 games in the Komodo - Stockfish superfianl match, Komodo leads by 4-1 with 55 draws. The last 10 games have been draws, mostly uneventful.

In game 51 the Komodo's eval jumped a little when Stockfish chose not to exchange pieces in the center. It took only a few moves for the eval to get back down, not clear what Komodo saw there. In the reverse game Stockfish had increasing evals up to 0.7,  chance to get a game back. After move 30 only the queens and rooks were left with pawns, both engines had an advanced passed pawn. However, when queens were exchanged and the passed pawns eliminated the evals plummeted to 0 in a drawn rook endgame.

Komodo held a small eval advantage for about 25 moves in game 53. The advantage disappeared as the pieces that were left started to be exchanged, until a drawn queen ending was reached. In game 54 Stockfish held the eval advantage longer, each engine staying behind almost static lines. When files started to open to a QRB vs QRN game, Stockfish had a passed pawn but Komodo countered with control over the 2nd rank. The threats balanced out to another draw.

In game 55 Stockfish seemed very cramped on the king side with many pieces and no room to move. Nevertheless it was an effective fortress which Komodo could only penetrate by exchanging pieces. By the time the black king was exposed it turned out that the white king was vulnerable to Stockfish's perpetual check, and a draw. Game 56 started with a series of captures that resulted in a RRB vs RRB endgame on move 17. The game continued until move 40 but the evals were 0 long before that.

In game 57 the center and queen side were blocked by pawns, and for a while it looked as though Stockfish as black had some pressure on the white king. The pressure evaporated after a few captures, and the pieces left could not move the pawn blockade, draw. In game 58 Stockfish again got a little excited with evals up to 0.5. Komodo's defense showed that Stockfish had nothing,  pawns again blocking any progress in a RRN vs RRN endgame.

In game 59 the center and king side were stablilized early in the game, and the queen side was used to exchange pieces. The remaining pieces stated to shuffle until the draw was declared. Game 60 reached a BNN vs BNN endgame in move 24, and then became a long shuffle contest since Stockfish kept a small positve eval. The eval decreased to 0 when the 50 move rule got close and the draw followed.


Monday, November 23, 2015

Season 8 superfinal, games 41-50

After 50 games, at the halfway point of the Komodo-Stockfish superfinal match, Komodo is leading 4-1 with 45 draws. Komodo increased its lead with another win, the chances of a Stockfish comeback are getting really low.

Game 41 got into an interesting imbalance where Komodo was down B vs RP but Stockfish couldn't castle and had badly placed pieces. At one stage Stockfish turned down a repetition twice, but had to give the exchange back. It still had a passed pawn but with the king exposed to queen attacks the game still ended in a draw. There were a few moves in game 42 where Komodo had a small eval advantage as black, but it faded quickly back to 0 and another draw, nothing to get excited about.

In game 43 Komodo kept a small eval advantage but could not realize it on the board. Evals came back to zero as the pieces came off the board, yet another draw. Game 44 featured almost 90 moves of shuffling in a RRB vs RRN position blocked by pawns, close to eight hours of waiting for the final draw.

Game 45 started with a small eval advantage for Komodo, but the evals soon dropped to zero, and this time the game ended quickly in a repetition. In game 46 all the pawns stayed on the board with the queen side blocked. Komodo gradually increased its eval with a little more space on the king side.

After some piece shuffling Komodo was able to realize its advantage by taking a pawn after the queens were exchanged.

Stockfish tried to trade pieces, eventually reaching an opposite color bishop ending with a pawn down, usually a sure draw.

However, in this position Komodo could hold the white king to defend the h pawn, and its king could walk safely to the queen side and attack the pawns there. Stockfish sttacked the black pawns on the king side with its bishop, still only one pawn down, but Komodo's pawns were better placed in the end.

Another win for Komodo, again in black, with opposite color bishops. Inconceivable! You get the feeling that Komodo is just better than Stockfish in this match.

In game 47 Komodo built an eval advantage which turned into an ending of BB vs BN. Stockfish had a beautiful defense, look at the position:

It's a bit like checkers. The light square bishop cannot penetrate, only be exchanged, and the dark square bishop can't do anything to white pieces. After a lot of shuffling Komodo exchanged a bishop for the knight, and for a few moves its evals shot up. It was a false alarm since although Komodo got to queen a pawn first, the only thing the queen was good for was stopping Stockfish from queening as well.

In game 48 Stockfish had two bishops and Komodo two knights, but all the rooks stayed on the board. This made the game much more drawish and it ended faster.

Game 49 was a little wild. Stockfish went for a king side attack, sacrificing two pawns and neglecting to castle. Komodo calmly counterattacked on the queen side, exchanging pieces when possible, then went for a combination that left RBB and pawns vs QN. The kings were so exposed that no progress could be made, so again a draw but at least interesting. Game 50 was also imbalanced, this time Stockfish sacrificed a knight for 3 pawns. Komodo maintained an eval advantage as black and tried to make use of its extra piece. However, by the time it got a pawn back the game was in a 7-man tablebase draw of RN vs RPP, adjudicating a few moves later.

Friday, November 20, 2015

Season 8 superfinal, games 31-40

After 40 games in the Komodo-Stockfish superfinal Komodo leads by 3 wins to 1, with 36 draws. Stockfish has finally won a game, showing that it is possible to beat Komodo, just very very hard. On the other hand Komodo added another win too, this time playing black. My feeling - Komodo is going to win this match.

Game 31 started with both queens moving forward unsupported, followed by a queen exchange as well as many other pieces captured. The game reached a double rook endgame on move 25, with equal material and where Komodo had an isolated passed pawn. Stockfish had no problem defending until all pawns were gone but one that couldn't advance, another draw. Game 32 was only a little different, reaching a RN vs RN endgame on move 26. All pieces were eventually captured, the game ended in a drawn king and pawns position.

In game 33 Komodo had a small eval advantage that didn't get anywhere. Once all the heavy pieces were exchanged Komodo's knights were a little more effective than Stockfish's bishops, but it still ended a draw. In game 34 there were no castlings and the pawns blocked all files except one. Stockfish had more room and an eval advantage but there was no way to improve. Instead both engines shuffled a lot with one capture to avoid the 50 move draw once. The game was adjudicated before the 50 moves were reached the second time.

In game 35 Komodo's king became very exposed but Stockfish had a 0 eval. Komodo was able to stabilize its position, and after rooks were exchanged the white king was much safer and the game drifted into a draw. Game 36 took a different path, Stockfish held to a small eval advantage and the heavy pieces remained on the board. At move 37 the position was:

Here Komodo decided to sacrifice a pawn, perhaps to gain initiative or to get rid of the white bishop pair that was gaining strength. A few moves later all the light pieces were gone and Komodo had to defend carefully to keep the b pawn from falling as well.

The eval started to increase gradually, but with all the heavy pieces playing it seemed that Komodo had enough to defend as well as threat the white king. The engines maneuvered for a long time until the queens were exchanged.

Now Stockfish's plan was getting clear, exchange pawns and keep the rooks. Indeed this is what happened, with Stockfish holding on to the connected e+f pawns.

This was a decisive advantage that the engines could not ignore, and even the most skeptic of fans had to realize that Stockfish was really winning. Finally, a sigh of relief. Stockfish with a clear win, without a lot of help from the opening. A score of 2-1 is very close and there are still many games to be played. This was a happy Stockfish moment.

Game 37 was very quiet, nothing special from either side and evals close to zero throughout the game. A draw adjudication was reached at the first possible opportunity. Game 38 started in a similar way, but around move 20 Komodo took the initiative and the evals became slightly negative. At move 30 Komodo had more space but the position looked blocked and the PV showed only shuffling.

After 20 shuffling moves Komodo broke the pawn structure with f6 and the board cleared up a little. Stockfish was getting low on time, and after the queens were exchanged Komodo's eval increased a little, what was it planning?

The black b pawn and the white c pawn were eliminated with a bishop exchange as well, and Stockfish (and its fans) started to feel the pressure. Komodo's plan was still not clear and material was equal but something was happening.

 Komodo placed the knight on f5, effectively defending its pawns while attacking the white h pawn. Meanwhile the black rook could attack pawns, the bishop or the king. Eventually Stockfish lost the d pawn, creating dangerous black pawns in the center.

As they started marching together Stockfish had no choice but to sacrifice the bishop to stop them, and the evals jumped accordingly.

The 8-piece ending was still very difficult and the game was adjudicated long before the mate was in sight. Komodo had to hang on to its remaining pawn to avoid a theoretical draw, but both engines agreed that the end result would be a Komodo win. Back to 3-1, so close to Stockfish's first victory Komodo produces a win in black. And the reverse game was so boring, where did this come from?

Games 39 and 40 were two relatively short uneventful draws. In both games the two engines had their kings exposed to attack, and when a threat became serious enough the other engine closed the game by perpetual checks.

Approaching the halfway point, the match is still quite close. Stockfish has shown it can win, but can it close the gap to Komodo? My gut feeling: no it can't. We'll know in about two weeks at the most.

Wednesday, November 18, 2015

Season 8 superfinal, games 21-30

After 30 games in the Komodo-Stockfish superfinal match Komodo is leading by 2 wins with 28 draws. The last 10 games have all been draws, but one of them was the most dramatic game of the season that everybody is talking about  in the chat and Stockfish forums ever since.

Game 21 started with a small eval advantage for Komodo. After a series of 11 consecutive capures the remaining pieces were QRR vs QRR with many pawns. This is a sure sign of a draw. Once the queens were off the evals reached 0 and the pawns were gradually removed until a tablebase draw was reached.
The reverse game 22 was a totally different story. The pieces stayed on the board for a longer time in a complicated position. The evals started to jump after Komodo went for a skewer attack with a bishop.

Really difficult to understand what is going on with all the pins and threats, but white could be losing an exchange immediately. And yet Stockfish's eval went up as pieces started to fall. After a while things settled down a bit.

Stockfish was an exchange down, but it was quite optimistic according to the eval. Was it seeing something that Komodo missed? The queen side pawns had potential but was this enough? It should be noted that the website was down for over three hours, so nobody saw the game live at this stage. The white eval gradually increased and Komodo's eval started to agree with this as well. When the live broadcast returned the Stockfish fans started to get excited, it looked like the first Stockfish win is near. The evals started to jump when rooks were exchanged.

Stockfish was over the 6.5 eval threshold a few moves later, having established a pair of connected passed pawns.

Komodo was still behind in eval but was rising as well. It was just a matter of time... Stockfish just had to be careful of potential check threats but it had it covered in the PV at least. Then - the website went offline again. So close to the end, it was clear that we won't see it live but the win was sure. When the website returned though - A DRAW, WHAT??? Nobody could believe it. The evals were over 26 for Stockfish and almost 5 for Komodo, and then Stockfish threw it away in this position:

The move played was Kg4, allowing Komodo to escape with checks. The post game consensus was that Bc2, which appeared in the Stockfish PV a few moves back, was a sure win. Nobody could explain this choice by Stockfish and the shock was total. The Stockfish eval function became a joke, and the overall feeling was that if it can't convert an eval of 26 then how will it win games at all in this match?

In game 23 Komodo had an isolated passed pawn but it was not enough for a win in the RB vs RB ending that was reached. In game 24 again Komodo had an isolated passed pawn, this time as black, this time the ending was of opposite colored bishops. The draw took a surprisingly long time, Stockfish kept its eval at 0.06 not allowing the adjudication rule to be applied.

Game 25 reached an RB vs RB ending on move 20. I don't know why the evals stayed positive, perhaps because white won a pawn later, but before long the evals dropped to zero resulting in a draw. In game 26 Stockfish managed to create an eval advantage of 0.6, Komodo's pieces had very little room to move. However, there didn't seem to be a plan for Stockfish to improve and then pieces started to be taken off. The rook ending was again a dead draw.

In game 27 Komodo seemed to have a promising attack on the black king but Stockfish countered on the queen side, sacrificed a bishop for pawns and got a perpetual check draw. In game 28 the evals dropped to zero much faster and the game reached a repetition without a lot of action.

In game 29 the line the engines chose led to a material imbalance of BN vs RP. Komodo had a small eval advantage of 0.5 that made Stockfish fans nervous again.

Stockfish managed to capture a bishop, at the price of letting Komodo queen a pawn which cost a rook.

In the ending Komodo's extra bishop let it eliminate some of the black pawns, but when all the white pawns were off the board the game was drawn. In game 30 Stockfish had a small advantage but the game progressed without material imbalances. towards the end Komodo sacrificed two pawns to open the white king position, and the game was adjudicated just before the perpetual checks started.