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!

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.

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.

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.

Brabo

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.

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.

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.

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. 

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. 

Brabo

Solution:
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#