Passed Pawns (endgame)

[Ralph Stoesser]

I also do not understand. Pe4 + Pd4 isn't a chain.

Pawn chain consists of pawns placed on the same diagonal, without interruption, so that only one of them is undefended. That pawn is called a base of pawn chain.

http://chessprogramming.wikispaces.com/Pawn+chain

[Eelco de Groot]

I also do not understand. Pe4 + Pd4 isn't a chain.

Pawn chain consists of pawns placed on the same diagonal, without interruption, so that only one of them is undefended. That pawn is called a base of pawn chain.

http://chessprogramming.wikispaces.com/Pawn+chain

It is for Stockfish though, if I understand it correctly, a pawn on rank_bb(r) is counted as a chained pawn, but the pawn that forms a base of a chain is not counted (for example e3 if there is also a pawn on d4 is a base pawn), you could defend that decision by stating a base pawn is a weak spot so not worth a bonus but it is also a very important pawn for the chain. So I consider that a weak spot in the code right now, the defence of a pawn base is non-existant in the code itself.

Regards, Eelco

Code: Select all

      // Member of a pawn chain (but not the backward one)? We could speed up
      // the test a little by introducing an array of masks indexed by color
      // and square for doing the test, but because everything is hashed,
      // it probably won't make any noticeable difference.
      chain =  ourPawns
             & neighboring_files_bb(f)
             & (rank_bb(r) | rank_bb(r - (Us == WHITE ? 1 : -1)));

[lech]

I am very sorry, I really don't understand what are you trying to say.

Perhaps I have understood. Are you suggesting the following patch ?

Code: Select all

       chain =  ourPawns
              & neighboring_files_bb(f)
-             & (rank_bb(r) | rank_bb(r - (Us == WHITE ? 1 : -1)));
+             & (rank_bb(r) | rank_bb(r + 1) | rank_bb(r - 1));

Yes, in common sense.
[d] 8/8/5p2/1p5p/1Pp5/2P2P2/6P1/8 w - - 0 1
the blocked pawns b5, c3 bonus =0
Pg2 – [!(theirPawns & file_bb(f))] - bonus /2 (?)
It was too absorbing work to improve the SF’s code, though an interesting new experience.
Good luck!
BTW: My last suggestion is: too high penalty for double isolated (x2) pawns [e.g. if (isolated & !doubled)].