Quote:
Originally Posted by PartyGirlUK
i) Most analysis engines showed black up between 1 & 2 pawns
If an engine shows the same value for the top 3 lines (e.g. -1.61 for all the 3), there's a high chance that, in fact, there's a drawing fortress. It's a well-known bug.
Engines evaluate positions at the end of a game tree basing on material advantage, open file possession, etc. In the fortress case, no matter the search depth, there will be almost the same position at each of the end leaves of the game tree and there will be no forced draw (no move repetition and no naked kings) as, from the engine's viewpoint, the side with the material advantage prefers to play on instead of repeating moves*. Engines don't check for the 50-move rule unless it's specified in the tablebase settings.
Here's a position from my own online game.
Stockfish correctly shows that Kxf5 is a losing move (White gets mated in 34) but it evaluates all the other king moves as -2.06 whereas it's obvious that Black can't break through then (either his king or his bishop has to shepherd the a-pawn, so he can't afford to sac the bishop for the f4 pawn).
Brag: my White opponent did take on f5, hoping to win
Beat: I should have finished him off much earlier instead of allowing him to pass the a-pawn.
* If an engine is told to avoid 50-move rule draws, then funny games can happen like
Nakamura vs Rybka (there's an epic troll ending).
Last edited by coon74; 11-16-2016 at 03:20 PM.
Reason: my and Naka's games added