Hi,
I am unable to play this position against Stockfish level 7 or 8 as white or black: rrrqkrrr/pppppppp/8/3PP3/3PP3/8/PPP2PPP/RNBQKBNR w KQkq -
However, I can play the starting position and this position: rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR w KQkq -
normally. I have noticed this problem both today and yesterday.
Thank you!
Help me please. This is a legitimate bug that has something to do with the nature of this position. I tried the position where white has played e4, d4, Nf3, Nc3, Bc4, and Bf4 and it worked as well. However something to do with changing blacks pieces to rooks and/or filling the white pawns in the middle causes the problem.
Guys I literally can't play any interesting positions, only stupid positions. Isn't board editor + play against computer supposed to work for all positions? Does it only work for legal positions? Can someone at lest give an explanation for why it doesn't work?
Near as I can tell, the issue is with putting more than eight pawns for either side. The analysis board still works for such positions, but you can't play them against the computer. Now that I've narrowed down the problem so much, can someone please do something? I've seen lots of other questions get answered since I made my initial post, including dumb en passant questions, and not a single response on this thread that poses a legitimate bug that is very annoying to anyone trying to play a position with more than eight pawns against the computer.
The position isn't possible in a chess game or in any supported variant. So i doubt its a bug.
Hello, it is a bit strange, I would say that it is because of the number of pawns too. But I tried another impossible position to check, and it worked:
IM Lovlas, I understand that it is not a legal position, but it's still interesting, and I just wanted to play it against the computer for fun. For example, setting up such positions can teach about strategic ideas that can then be applied to other games. Even if I'm the only one using the feature this way, I'd still like an answer as to why it doesn't work because it doesn't make sense to me that this type of position doesn't break the analysis board, but it does break the play vs computer feature.
Demonolith, thank you for your help. It would be nice to get a perspective from a Lichess moderator as to what the difference is. If it's a coding thing that can be easily resolved, I'd like that. If not, I totally understand.
In general, Stockfish's behavior is undefined for invalid input, and parts of the code assume that there are not more than 8 pawns per color (and no pawns on the back ranks, etc.), so it is reasonable to not let it run on illegal positions since it might crash.
As #8 says the behavior is undefined.
You could change the code to make some of these positions work however noone ever tested what Stockfish would do then. (and noone will test it as it's unnecessary for realy play)
So it might just output nonsense without the human necessarily realizing that. Thus instead of doing that it just doesn't analyze such impossible positions.
As for the other impossible position. While I don't know what's up with that pawn on b1, the rest of the position is not a problem with normal Stockfish since Stockfish knows how to play with a normal piece set, no matter how they are positioned. (e.g. most chess960 positions are impossible to reach from the normal chess starting position however it's essentially still the same game; but e.g. playing with 17 knights vs 10 queens is not)
Not to speak of some internal data structures which might simply not work how they should if there are more than 10 rooks. (which could happen in the first game)
K, I just don't get the difference because I can set up the initial 16 pieces in weird ways and Stockfish still plays quite well. Also, the analysis feature provides moves that are at least logical. Shouldn't it be up to the human to realize that Stockfish isn't working probably, as opposed to inserting extra code to completely destroy what might just be a bit broken. Still, if noone else wants this, I can see why it isn't a big deal to others. I just thought it would be fun.
