Stockfish can't evaluate the KP vs K endgame?

[Zhu.Jianzhao]

What version did you use? I tried some of the recent compiles and SF sees a loss for black (after Kf6).

I tired Stockfish 2.3.1 JA just now, got the same problem, it returns 0.00 after I entered Kf6.

[Uri Blass]

Nothing to do with evaluation of pawn endgames.

It is obvious that it is about evaluating first repetition and many engines evaluate first repetition as a draw because they are designed to play and not to analyze correctly and the programmers did not want to add code that is probably not productive for playing strength.

It is a disadvantage of the program but
I do not think that it is a bug because a bug is a behaviour that is different than the intention of the programmer.

[Zhu.Jianzhao]

Stockfish 20-02-13

Where to get it? Do you have a link?

from http://rybkaforum.net/cgi-bin/rybkaforu ... pid=462595

[mar]

I tired Stockfish 2.3.1 JA just now, got the same problem, it returns 0.00 after I entered Kf6.

Yes Miguel is right - it's a repetion problem.

Code: Select all

position fen 6k1/8/6K1/6P1/8/8/8/8 w - - 0 1 moves g6f6

However, SF would never play Kf6 in the first position anyway. Not a bug then.

[michiguel]

I tired Stockfish 2.3.1 JA just now, got the same problem, it returns 0.00 after I entered Kf6.

Yes Miguel is right - it's a repetion problem.

Code: Select all

position fen 6k1/8/6K1/6P1/8/8/8/8 w - - 0 1 moves g6f6

However, SF would never play Kf6 in the first position anyway. Not a bug then.

It does not matter whether the engine plays Kf6 or not, if it is used to analyzed a game, it will give wrong results for positions with a repetition in its path.

Miguel

[JVMerlino]

I tired Stockfish 2.3.1 JA just now, got the same problem, it returns 0.00 after I entered Kf6.

Yes Miguel is right - it's a repetion problem.

Code: Select all

position fen 6k1/8/6K1/6P1/8/8/8/8 w - - 0 1 moves g6f6

However, SF would never play Kf6 in the first position anyway. Not a bug then.

It does not matter whether the engine plays Kf6 or not, if it is used to analyzed a game, it will give wrong results for positions with a repetition in its path.

Miguel

So this is an analysis bug only, IMO. Most engines give a draw score in the search after one repetition to (barely) improve speed, right? I wonder if Bob would do a cluster run to see if one repetition has any noticeable ELO improvement compared to requiring two reps?

Anyway, my engine does the same thing. Seems like the easiest way to resolve this is to require two reps when in analysis mode, and only one rep when playing a game (on the assumption that the speed increase has value). "Bug" fixed.

jm

[mar]

It does not matter whether the engine plays Kf6 or not, if it is used to analyzed a game, it will give wrong results for positions with a repetition in its path.

Miguel

Yes, but detecting true 3-fold repetitions won't help in general because there is TT. This problem hasn't been solved yet AFAIK. Recently, there was a thread about a new approach (I don't remember), where the authors worked with paths I think. It would be awesome if this problem could be solved without loss of speed, but I fear this is not the case.

[michiguel]

I tired Stockfish 2.3.1 JA just now, got the same problem, it returns 0.00 after I entered Kf6.

Yes Miguel is right - it's a repetion problem.

Code: Select all

position fen 6k1/8/6K1/6P1/8/8/8/8 w - - 0 1 moves g6f6

However, SF would never play Kf6 in the first position anyway. Not a bug then.

It does not matter whether the engine plays Kf6 or not, if it is used to analyzed a game, it will give wrong results for positions with a repetition in its path.

Miguel

How do you know you are analyzing? you can't. If the engine is used with another tool to annotate the game, I cannot see how that could be done. IMHO, this is not a bug, but a flawed optimization.

Miguel

So this is an analysis bug only, IMO. Most engines give a draw score in the search after one repetition to (barely) improve speed, right? I wonder if Bob would do a cluster run to see if one repetition has any noticeable ELO improvement compared to requiring two reps?

Anyway, my engine does the same thing. Seems like the easiest way to resolve this is to require two reps when in analysis mode, and only one rep when playing a game (on the assumption that the speed increase has value). "Bug" fixed.

jm

[Michel]

GNU Chess uses the single repetion rule only for repetions occurring within the search. For repetitions involving the games history it uses the threefold repetition rule. So it analyzes this position correctly.

[JVMerlino]

So this is an analysis bug only, IMO. Most engines give a draw score in the search after one repetition to (barely) improve speed, right? I wonder if Bob would do a cluster run to see if one repetition has any noticeable ELO improvement compared to requiring two reps?

Anyway, my engine does the same thing. Seems like the easiest way to resolve this is to require two reps when in analysis mode, and only one rep when playing a game (on the assumption that the speed increase has value). "Bug" fixed.

jm

How do you know you are analyzing? you can't. If the engine is used with another tool to annotate the game, I cannot see how that could be done. IMHO, this is not a bug, but a flawed optimization.

Miguel

Winboard's "analyze" command puts the engine in analysis mode. Does UCI not provide a similar command?

jm