Friday, November 15, 2013

Stockfish 4

Last month I was triggered by hypekiller5000 that a new release of Stockfish became available and scored remarkably well on the ccrl (computer chess rating list) with a 3rd place. Important detail is that the program can be downloaded for free. Now I am always a bit reluctant to use free software as I immediately think about illegal copies but eventually I let myself seduce to test and use the program in my analysis. The main reason for this is that my method of analyzing is based on 2 engines (see blogarticle analyseren met de computer) and with such method of analyzing it is recommended to use 2 approximately equal engines (preferably also complementing engines). Last year I wrote on this blog that I bought  Houdini 2.0, which replaced Fritz 11. As a consequence Rybka 3 remained as second engine but I quickly experienced that the gap in strength between the 2 engines became too big to have a good return with my method of analyzing. We should not forget that the release-date of Rybka 3 was august 2008 so we may state that the expiry-data has been passed.

The first thing which stands out from Stockfish is the way how the engine evaluates the positions. If you are used to classical evaluations of Rybka, Fritz and Houdini then you are in for some surprise. I mean with Stockfish you can easily have evaluations which divert 1 or even more pawns (so 100/100sten). An absolute record I detected in an analyzed variation of my recent game against Steven Geirnaert, see below screenshot.
Stockfish shows an evaluation of 94 points for black !

Stockfish shows an advantage of 94 points for black. Even if you promote all the remaining pawns then still you can't reach this sum. Houdini by the way only shows 11 points advantage for black after 10 minutes calculating. On chesspub this fact was mentioned as a negative quality of Stockfish but I believe this needs to be nuanced.  The program is in the first place made to play as strong as possible and uses therefore a mechanism for the evaluations which helps optimal. These evaluations are shared pure informative to the end-users but it is never the intention to make a final judgement of the position about who has the advantage and how big it exactly is. 

One would expect with such high evaluations that the engine will be very strong in tactics. However comparing with Houdini then I notice it is considerably weaker. Especially with quiet unexpected sacrifices Stockfish seems to have troubles. The solution of the below analyzed variation is found within a second by Houdini but after 10 minutes Stockfish still didn't!
[Event "Analyzed variation Groffen - Brabo"] [Date "2013"] [SetUp "1"] [FEN "r4r1k/1p5p/p1p1b3/3pPp2/1P1Q1P2/4P1R1/q6P/2R2BK1 w - - 0 23"] [PlyCount "9"] 23. e4 $3 {(Stockfish misses this move completely despite the fact that Houdini finds it very quickly.)} Rg8 (23... dxe4 24. Bc4 Bxc4 25. e6 Rf6 26. Qxf6#) (23... Rf7 24. exf5 Rxf5 25. Bh3 Rh5 26. f5 $18) (23... fxe4 24. Bh3 Rae8 25. f5 Rg8 26. Bg4 $18) 24. exf5 Rxg3 25. hxg3 Bxf5 26. g4 Be4 (26... Bxg4 27. e6 Kg8 28. Qe5 $18) 27. Re1 $1 $18 *'/>
It is incredible that Houdini finds this breakthrough-move e4 so quickly and correctly calculates the consequences. Besides, the keymove reminds me on the only time that I was completely surprised by my opponent in my correspondence-career (20 games played in the period 1998-2003). With some trouble I still escaped with a draw.
[Event "EU/M/1234"] [Date "1998"] [White "Verhoef, H."] [Black "Brabo"] [Result "1/2-1/2"] [SetUp "1"] [FEN "q5k1/1r4p1/r1pbp2p/P2p1p2/3P4/P5P1/3QPPBP/R1R3K1 w - - 0 27"] [PlyCount "47"] 27. e4 $3 {(This move was a complete surprise for me. Houdini shows this move immediately but Stockfish needs on my desktop still more than 4 minutes.)} fxe4 28. Bf1 Rxa5 29. Rxc6 Bxa3 30. Bh3 Kh8 31. Bxe6 Rb2 32. Qc3 Rb8 33. Rc5 Rxc5 34. dxc5 Qc6 35. Bxd5 Qxc5 36. Qxc5 Bxc5 37. Bxe4 {(The worst is over and I have little trouble to make a draw.)} Rf8 38. Ra2 g5 39. Kg2 Kg7 40. f3 Rd8 41. h4 gxh4 42. gxh4 Rf8 43. Kh3 Rf4 44. h5 Be7 45. Ra7 Kf8 46. Kg2 Bg5 47. Bg6 Kg8 48. Rd7 Kf8 49. Kf2 Kg8 50. Ke2 1/2-1/2'/>
Again Houdini finds the move instantly ( in 1999 this move never popped up on the screen) while Stockfish still needs more than 4 minutes. I still can show other tactical examples (eg. 8.g4 in my article on Houdini 2.0) but I assume that in the meantime it is sufficiently clear. Stockfish cuts a lot in the tree of variations to make an evaluation which causes it to regularly miss some tactic. Now how is it possible that there is only a gap of 25 points with Houdini, looking to the elo-rankings of the engines? Well clearly there is more than just tactics. It is very difficult to quantify but looking how Stockfish plays in stonewall-positions, I notice that the engine better understands than Houdini which plans are possible. On the other hand, in positions with fixed pawnchains as e.g. in the Portisch Hookvariant I notice no real difference in strength with Houdini. I deduct that pawnmoves could be a very important subset of how the mechanism for evaluating works of Stockfish.

As expected this effect is enlarged in the endgame. This is also confirmed in my first analyses. In this phase Stockfish overpowers completely Houdini. First I show an analyzed variation from my game against Raetsky which I briefly already mentioned in my previous article.
[Event "Analyzed variation Raetsky - Brabo"] [Date "2005"] [SetUp "1"] [FEN "R1bB2k1/6pp/4p3/2N2p2/1p1P4/4P1P1/5PKP/2r5 b - - 0 37"] [PlyCount "49"] 37... Rxc5 38. Ba5 Rc4 39. Bxb4 Kf7 $1 {(Stockfish chooses to keep the bishops on the board which looks to me as the rigth choice.)} (39... Rxb4 $6 { (Houdini chooses for the rook-endgame but with 10 seconds per move can not hold the position.)} 40. Rxc8 Kf7 41. Rc7 Kf6 42. Rc6 Kf7 43. h4 Rb2 44. h5 h6 45. Rc7 Kf6 46. Kf3 Rd2 47. Ra7 Rb2 48. Ra6 Rd2 49. Ra8 Kg5 50. Rg8 Kf6 51. Rf8 Ke7 52. Rc8 Kf6 53. g4 fxg4 54. Kxg4 Ra2 55. Kf3 Ra3 56. Rc5 Rb3 57. Rc6 Kf5 58. Ke2 Rb2 59. Kd3 Rb3 60. Kc4 Ra3 61. e4 Kxe4 62. Rxe6 Kf5 63. d5 Ra2 64. f3 Rc2 65. Kd4 Rh2 66. Re4 Kf6 67. d6 Kf7 68. Kd5 Rxh5 69. Kc6 Rh1 70. d7 Rc1 71. Kd6 Rd1 72. Kc7 Rc1 73. Kd8 g5 74. Re7 Kf8 $18) 40. Ra7 Ke8 41. Bd6 Bd7 42. h4 Bc6 $1 {(To restrict the activity of the white king seems indeed the best choice to me.)} ( 42... Rc2 $6 {(Houdini chooses to hang on the f-pawn but gets later into problems once white decides to sacrifice that pawn.)} 43. Kf3 h6 44. h5 Bc6 45. Kf4 Rxf2 46. Ke5 Bd5 47. Rxg7 Re2 48. Kf6 Rc2 49. Re7 Kd8 50. Rh7 f4 51. Bxf4 Rc6 52. Ke5 Ke8 53. e4 Bb3 54. Rxh6 Ra6 55. d5 Kf7 $18) 43. Kf1 Bf3 44. Ke1 Rc2 45. Re7 Kd8 46. Rxg7 Re2 47. Kf1 Rb2 48. Bc7 Ke8 49. Ke1 Re2 50. Kd1 h5 51. Bd6 Kd8 $1 {(Only after 4 minutes calculating, Houdini understands winning material with Rxe3 is not optimal.)} (51... Rxe3 $6 52. Kd2 Re2 53. Kd3 Kd8 54. Be5 Rxf2 55. Ke3 Rf1 56. Kf4 Bg4 57. Kg5 Rc1 58. Kf6 Rc6 59. Rh7 Bd1 60. Kg5 Rc1 61. Bf6 Ke8 62. Re7 Kd8 63. Rxe6 Kd7 64. Re1 Kd6 65. Be5 Kd5 66. Rf1 Ra1 67. Rxf5 Ra2 68. Bg7 Ke6 69. Rc5 Bf3 70. Kf4 Rf2 71. Re5 Kd7 72. Ke3 Rf1 73. Rf5 Bg2 74. Rxh5 Rf3 75. Kd2 Rxg3 76. Be5 Rb3 77. Rg5 Be4 78. h5 Rh3 79. Bg7 Ke7 80. h6 Kf7 81. Re5 Bh7 82. Ke2 Bd3 83. Kf2 Bh7 84. Rb5 Be4 85. Rb6 Kg8 86. Re6 Bd5 87. Rd6 Rh5 88. Be5 Bf7 89. Rb6 Bd5 90. Kg3 Bc4 91. Bf4 Kf7 92. Rc6 Bd3 93. Rc5 Bf5 94. d5 Bd7 95. Kf3 Kg6 96. Ke4 Rf5 97. Rc7 Rf7 98. Ke5 Rf5 99. Kd6 Rxf4 100. Kxd7 $18) 52. Kc1 Rxf2 53. Rh7 Re2 54. Bf4 Ra2 55. Bc7 Ke8 56. Bd6 Kd8 57. Be5 Re2 58. Bf6 Kc8 59. Bg5 Rg2 60. Bf4 Kd8 61. Rc7 Be4 {(The king is an important piece in the endgame but here he is cut off. As a consequence, the extra pawn is insufficient to force the win.)} *'/>
3 times Houdini loses the endgame while Stockfish marvelously defends (which doesn't mean that I claim that the endgame is for sure a draw against perfect play). Also in the 2 endgames discussed in my blogarticle on Houdini 2.0 Stockfish is clearly superior. 42...Th4! is found by Stockfish within seconds while Houdini 2.0 needs more than 3 minutes. Houdini 2.0 doesn't find the brilliant 48...Kd5! while Stockfish again does in about 7 minutes. However Shirovs brilliant Bh3 seems again a bit too hard for Stockfish as after 10 minutes it is still not found but of course here we are again talking about tactics.

Meanwhile it is for me clear that the program very well complements with Houdini 2.0. I am surprised that such strong program is offered for free. On the other hand I also realize that a collective of volunteers often presents better results than 1 or 2 professionals. Moreover it is expected that the next release of Stockfish could very well be the new number 1 in computerchess. No need to panic as we are still extremely far from solving chess so there still remains many years of pleasure to search for the unknown.


Tuesday, November 12, 2013

Problem moves

A spectacular game with a number of tactical blows will normally more appeal the audience than a more positional played game. Sacrifices and counter-sacrifices are not only fascinating but often also much easier to understand than the so called quiet moves. It is no coincidence that I chose in my blogarticle mijn mooiste zet for only tactical positions. Explaining well the concept of critical moves, is not easy with quiet moves which often differ little or nothing with the alternatives.

Nevertheless I won't deny that I can also enjoy a lot the quiet moves. As there are often in a game many of them which are trivial, it is not redundant to describe what can be a beautiful quiet move. In my opinion the most important characteristic is that the move must be rare and at the same time functional. Recently I bumped via the blog of David Smerdon on a game between L'Ami-Krasenkow in which the remarkable move Bh8-a1 was played.
[Event "Unive Open"] [Site "Hoogeveen NED"] [Date "2013.10.21"] [Round "4.2"] [White "Erwin L’Ami"] [Black "Mikhail Krasenkow"] [Result "1/2-1/2"] [ECO "D31"] [SetUp "1"] [FEN "3r3B/5k1p/8/p7/Rp6/8/6PP/6K1 w - - 0 36"] [PlyCount "56"] 36. Ba1 {(A retreating bishop move on the long diagonal is a rare move in practice. White gets a big advantage wit this move but eventually does not manage to win the game.)} Rd1 37. Kf2 b3 38. Kf3 Rd2 39. Rf4 Kg8 40. Rg4 Kf8 41. Bg7 Kf7 42. Bh8 Rd8 43. Rg7 Ke6 44. Rxh7 a4 45. Rh6 Kf7 46. Bb2 Rd2 47. Rh4 Rxb2 48. Rxa4 Rc2 49. Rb4 Rc3 50. Kf2 Rc2 51. Kg3 Rc3 52. Kh4 Rc2 53. Kh3 b2 54. Rb6 Ke7 55. g4 Kd7 56. Kg3 Kc7 57. Rb3 Kd6 58. Rb8 Kc5 59. h3 Kc4 60. Kf4 Rd2 61. Rc8 Kd3 62. Rb8 Kc4 63. Rc8 Kd3 1/2-1/2'/>
A bishop in the corner has a minimum of squares to where it can move to. So moving a bishop on purpose from one corner to the other one, is not what we see every day on the board. Thanks to an old article of the fantastic website of  Tim Krabbe we know that this move happens once per x thousands of games. Next would be nice to know which move is the most rare one. Well except some minorpromotions all moves have been played at least once in practice. This with the restriction if we use the long notation. If we use the short notation then I am not so sure of that even if we don't take minorpromotions into account. 

A knight on the rim is grim, is a known proverb so we won't play a knight easily to the side of the board. Putting a knight in the corner is obviously even less done although not very rare as Herman Grooten recently illustrated in some articles on schaaksite: vier maal een paard op h1 en gespot 56 paard naar de hoek. Really weird it is when you put a knight in the corner when you have the choice between 2 knights. I mean you play a move like Nba8, Nca8, Ngh8, Nfh8, Nca1, Nba1, Nfh1, Ngh1. I played such move once in my career against Alexander Raetsky whom after the tournament became grandmaster.
[Event "Open Cappelle La Grande 7de ronde"] [Date "2005"] [White "Raetsky, A."] [Black "Brabo"] [Result "1-0"] [ECO "A85"] [WhiteElo "2460"] [BlackElo "2316"] [SetUp "1"] [FEN "2r3k1/1bn3pp/pn2p3/B3Np2/3P4/6P1/4PP1P/R4BK1 b - - 0 30"] [PlyCount "16"] 30... Nba8 {(Black has already a bad position so I do not find Nba8 much sillier than Nbd5 which would block blacks bishop. My opponent did not agree at all while the engines show little difference in evaluation between both moves.)} 31. e3 Nb5 32. Nd3 Rc2 $6 {(A try to become active but objectively it only worsens the position. )} 33. Nc5 Bc8 34. Bxb5 axb5 35. Bd8 b4 36. Rxa8 $2 {(The logical followup but there is a hidden resource which white misses. E.g. Ra7 would be over and out.)} b3 $2 {(With very little time remaining, I miss a golden opportunity.)} (36... Rc1 $1 37. Kg2 Rxc5 { (A complex endgame in which black has good surviving chances.)}) 37. Nxb3 Bb7 38. Ra1 1-0'/>
After the game my opponent laughed in my face for the most idiotic move he ever saw although even today I still don't find it a bad choice. Anyway at move 36 I missed a beautiful drawing chance with Rc1 followed up with Rxc5. Now I do admit that with such moves you won't win many games. The former worldchampion Anatoly Karpov succeeded once with such sort of move but he was at that time still very young see his 29th move Nfh1 against Fedin. Of the 8 possibilities, I found 7 but I assume Nba1 is likely also once played. A lot more unlikely it becomes if we add the condition that the move can't be played on the own side of the board. I mean Nba8 for white instead of black. Out of curiosity I challenge the reader to find such example from the tournamentpractice (so without cheating and constructing a game.) 

So far the special moves but really nice things can be seen when several quiet moves are combined. Recently Luc Winants deservedly informed us about a nice moment at move 31 and 32 in his game against Moens.
[Event "European Club Cup"] [Site "Rhodes GRE"] [Date "2013.10.23"] [Round "4.11"] [White "Andreas Moen"] [Black "Luc Winants"] [Result "0-1"] [ECO "C79"] [WhiteElo "2390"] [BlackElo "2534"] [SetUp "1"] [FEN "3rr1k1/5qpp/2pBbp2/1pP5/p3PP2/2QR2R1/1P4PP/6K1 b - - 0 31"] [PlyCount "5"] [EventDate "2013.10.20"] 31... Ba2 {(Not the only possible move but a move which contains some poison and includes a very nice theme. )} 32. Rde3 Qb3 {(A bristol-clearance which is rarely seen in practice. )} 33. Qxf6 $4 Qxe3 0-1'/>
We may rightly speak here about a bristol clearance. A lighter piece clears space for a heavier piece. In the problemworld this is well known but in practice you see such things very rare. A step further goes the below analysed opening in which i already discovered in 1997 a lovely novelty. If I can trust my databases then the move is still not played in practice. 
[Event "BEL-ch Expert"] [Site "Namur"] [Date "2007.06.30"] [Round "1"] [White "Akhayan, Ruben"] [Black "Hovhanisian, Mher"] [Result "0-1"] [ECO "C11"] [WhiteElo "2247"] [BlackElo "2391"] [PlyCount "110"] 1. e4 e6 2. d4 d5 3. Nc3 Nf6 4. e5 Nfd7 5. f4 c5 6. Nf3 Nc6 7. Be3 Qb6 8. Na4 Qa5 9. c3 cxd4 10. b4 Nxb4 11. cxb4 Bxb4 12. Bd2 Bxd2 13. Nxd2 b5 14. Nb2 Nc5 15. Bd3 Qc3 {(The move was around 1997 pretty popular with players in the region of Bruges. )} 16. Bxb5 $6 {(The only move in practice which has been tested several times but the novelty which I discovered in 1997 is stronger. )} ( 16. Qb1 $1 $146 {(A turton-bristol clearance as the queen clears space for the rook of h1.)} Bd7 17. Ke2 f6 18. Rc1 Qa3 19. Nb3 Rc8 20. exf6 gxf6 21. Kf1 Kf7 $14) 16... Bd7 17. Bxd7 Nxd7 18. Na4 Qe3 19. Qe2 Qxf4 20. Rf1 Qxe5 21. Qxe5 Nxe5 22. Nf3 Nxf3 23. gxf3 Ke7 24. Kd2 Rhc8 25. Rab1 Rc7 26. Rfc1 Rac8 27. Rxc7 Rxc7 28. Kd3 g5 29. Rb5 Kd6 30. Ra5 Ke5 31. Nc5 h5 32. Nb3 Rc3 33. Ke2 Rc2 34. Kd3 Rxh2 35. Rxa7 f5 36. Nxd4 Rh1 37. f4 gxf4 38. Nf3 Kf6 39. a4 h4 40. Rh7 h3 41. Rh6 Kg7 42. Rxe6 h2 43. Nxh2 Rxh2 44. Rd6 Ra2 45. Rxd5 Kf6 46. Rd8 Kg5 47. Rg8 Kh4 48. Rh8 Kg4 49. Rg8 Kf3 50. Ra8 Kg2 51. Rg8 Kf2 52. Ra8 f3 53. Kc3 Kg3 54. Rg8 Kf4 55. Kb3 Ra1 0-1'/>
Here the heavier piece clears space for the lighter piece. In my old book of problems this is called a Turton-Bristol but I also found different names so there is discussion about what is the right name. Finally I also want to show a real problem which I built 20 years ago as a non clubplayer. There exist many more beautiful creations with this theme but it sounds to me anyway appropriate in the context of the blogarticle. The solution is mentioned on the bottom of the article as maybe some readers prefer to try first themselves although I expect it must be easy if you read this article.
Wit mates in 3
I strongly doubt that such problemmoves are possible in tournament practice. Anway schaakcompositities clearly show that chess hides many more possibilities than we will ever see in a boardgame. Therefore I also think that we shouldn't search too fast for the rare/ problem-moves in a game. It is not with that sort of moves that we will decide a game in our favor or you have to be a very strong player like the grandmasters in above examples. 


Loydse clearance: A piece clears space for another piece which uses it in the opposite direction.
1.Lh8 (dreigt Db2#), Kb7 2.Dg7+ Kb6 3.Db2#