4 ms·

He did find a move that occurred a single time including the specific game that included it. He also showed many moves that occurred zero times from every sing

by Retric 2y ago

He did find a move that occurred a single time including the specific game that included it. He also showed many moves that occurred zero times from every single game played on lichess.org. So, depending on your definition either could reasonably qualify. Which you pick as the rarest is simply an arbitrary definition. You could consider different notions, but run into the issue of defining what is unambiguous. IE You could say e2 to e4 is unambiguous for a given game state but that would imply game state must be included in the definition for of a move. Defining what the minimum game state is for an unambiguous move would be a video of its own.

zarzavat 2y ago
What occurred once is not what chess programmers would call a “move”, but rather what chess players would call “move”. His definition of a move is one ply of algebraic notation. From a chess programming perspective algebraic notation is just a data format and doesn’t have any greater significance. In programming terms a move is a data structure that allows you to derive one position from another according to the rules of chess. In Stockfish a move is a 14 bit number, the first 5 bits are the destination square, the next 5 bits are the origin square, the next 2 bits are the promotion piece, and the last 2 bits are the move type (normal, promotion, en passant or castle)
- maverwa 2y ago
  I was wondering on how Stockfish encodes the destination and origin square in 5 bits each. I think they don't, at least the code on github uses 6 bits each, which actually gives you 64 possible values, so works out fine: https://github.com/official-stockfish/Stockfish/blob/master/src/types.h#L351-L361 https://github.com/official-stockfish/Stockfish/blob/master/... Thats 16 bits. Thank you for sending me down that (small) rabbit hole!
  - zarzavat 2y ago
    Yes you are correct, I had 2^5 = 64 in my head for some reason.
- Retric 2y ago
  Comparing games with that notation alone would make moving your queen e2-e3 in game A the same as moving a pawn e2-e3 in game 2. I don’t think anyone would actually agree those are the same move. What Stockfish considers a move includes the full board state, it simply doesn’t need to pass that information around internally. Thus removing that ambiguity but means there’s a great number of moves that have only occurred once. Also, it’s 6bit + 6bit + 2bit + 2bit = 16 bits which isn’t an arbitrary number. There’s no need to actually encode that something is a promotion because it can be inferred from the board state, but there’s zero cost to pass an extra bit around so it’s included anyway.
- deleted 2y ago
  [deleted]

by Retric 2y ago

zarzavat 2y ago

What occurred once is not what chess programmers would call a “move”, but rather what chess players would call “move”. His definition of a move is one ply of algebraic notation. From a chess programming perspective algebraic notation is just a data format and doesn’t have any greater significance. In programming terms a move is a data structure that allows you to derive one position from another according to the rules of chess. In Stockfish a move is a 14 bit number, the first 5 bits are the destination square, the next 5 bits are the origin square, the next 2 bits are the promotion piece, and the last 2 bits are the move type (normal, promotion, en passant or castle)

maverwa 2y ago
I was wondering on how Stockfish encodes the destination and origin square in 5 bits each. I think they don't, at least the code on github uses 6 bits each, which actually gives you 64 possible values, so works out fine: https://github.com/official-stockfish/Stockfish/blob/master/src/types.h#L351-L361 https://github.com/official-stockfish/Stockfish/blob/master/... Thats 16 bits. Thank you for sending me down that (small) rabbit hole!
- zarzavat 2y ago
  Yes you are correct, I had 2^5 = 64 in my head for some reason.
Retric 2y ago
Comparing games with that notation alone would make moving your queen e2-e3 in game A the same as moving a pawn e2-e3 in game 2. I don’t think anyone would actually agree those are the same move. What Stockfish considers a move includes the full board state, it simply doesn’t need to pass that information around internally. Thus removing that ambiguity but means there’s a great number of moves that have only occurred once. Also, it’s 6bit + 6bit + 2bit + 2bit = 16 bits which isn’t an arbitrary number. There’s no need to actually encode that something is a promotion because it can be inferred from the board state, but there’s zero cost to pass an extra bit around so it’s included anyway.
deleted 2y ago
[deleted]