Monday, February 8, 2016

Fortresses

Maybe the last stand in standardchess in which we can beat the computer is to recognize and build fortresses. There exist a lot of definitions for fortresses but in this article I stick to endgames (maximum 4 pieces besides pawns and kings) in which material is sacrificed to defend successfully. Some trivial endgames like rook-pawn + bishop of the wrong colour are evaluated correctly by our current engines but a fortress like in the high-class game Shakhriyar Mamedyarov - Fabiano Caruana created a lot of confusion.

Commentators initially thought that Fabiano blundered and even after the game some players weren't convinced about the fortress, see chessbomb or the blog of James Stripes. Today we are so dependent and addicted to evaluations of our engines that we don't question them anymore. Personally I only believe a score of +5 or a tablebase-hit that a win is 99,99% certain as I described earlier in my article to analyze with engines. Setting +5 is really not too high as some time ago the scores went up high while analyzing an endgame with Stockfish and Komodo while eventually they didn't manage to find the killer.

The finalgentool can't judge the final position but with the help of HK5000 I got to know that it is indeed a draw after he checked the lomonosov 7 men tablebases. Yes indeed scores of +4,2 for Stockfish and +2,8 for Komodo don't mean there is a win. You don't expect that immediately of the current leaders which are considered generally invincible. I also expect that these are no records even if we don't take special positions into account from the world of compositions. Komodo even showed a personal higher score of +3,2 in the fortress which I met in my analysis of move 42 in my game against Stone, see my article bricks. Do you know fortresses from practice which are evaluated even worse then write it down in a reaction below this article !

On the other hand above analysis of both fortresses also show that engines can still discover a lot of interesting lines. Not seldom a strong engine can crack a fortress by using some very complicated constructions. I had a look to the so-called fortress which appeared in the marathon-game of 122 moves in the last world-championship. Neither Carlsen nor the commentators found a win in the 7th game but thanks to Lets Check I still found a weak spot.

I looked on the web for serious analysis of this endgame but I didn't find much. The only exception was the remarkable study of the Russian grandmaster Pavel Maletin on the site of the Russian chessfederation but it is not very readable and he admits that improvements are possible. I am curious if some other analysis exists but who wants to stick out their neck? I expect that even Kasparov would need a lot of time to make a decent analysis as published in his world-championship books.

While preparing this article, I also reviewed some analysis of fortresses popping up in my older games. No surprise here too as I also found some holes in the analysis. I mentioned in my article the Spanish with d5 that a fortress exists in the analysis of move 50 of my game against Fabien Libiszewski. Stockfish must move heaven and earth but in the end manages to breakthrough.

Later I did find an improvement for white just before the start-position by playing immediately 64.Rxf3+. That avoids the black king running to h4 and chasing away the white king out of the corner. If white positions the rook on g2 and the king on g1/h2 then it is although a fortress but that doesn't matter in this story. Fortresses are often too abstract for our engines but that is not the same as engines are useless to analyze fortresses. There is continuous progress made but fortunately still some mystery remains for a while.

Brabo

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