Author: Alessandro Damiani
Date: 02:17:49 09/25/98
Go up one level in this thread
On September 24, 1998 at 11:43:38, Robert Hyatt wrote: >In the ICCA Journal, Vol. 16, No. 4, GM Timoshchenko is comparing various >chess programs on how they evaluate bishops vs knights. He gives several >positions, with this one being the most interesting at present: > > > +---+---+---+---+---+---+---+---+ > 8 | | | | | | | *K| | > +---+---+---+---+---+---+---+---+ > 7 | *P| *B| | | *B| *P| *P| | > +---+---+---+---+---+---+---+---+ > 6 | | | | | *P| | | *P| > +---+---+---+---+---+---+---+---+ > 5 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > 4 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > 3 | | | N | | P | N | | P | > +---+---+---+---+---+---+---+---+ > 2 | P | | | | | P | P | | > +---+---+---+---+---+---+---+---+ > 1 | | | | | | | K | | > +---+---+---+---+---+---+---+---+ > a b c d e f g h > > >fen: 6k/pb2bpp1/4p2p///2N1PN1P/P4PP/6K/ w - - > >Here is the gist... to feed this to a program and with no searching, >see how it evaluates this. Chessmaster 2100 says -.26, Fritz-2 says -.47, >and chess-genius 1.0 says -.48. I recently fixed two "holes" in Crafty's >evaluation, one concerning "if you have one bishop in the ending, get your >pawns on the *other* color squares" and the other "if in an endgame, with >pawns on both wings, a bishop is significantly better than a knight." > >This last influences the evaluation of the above position quite markedly, >because this is an endgame, and black is going to get the bishop-over- >knight in endgame bonus two times since black has two bishops, white has >none. Black also gets the traditional bishop-pair bonus as well, which >might or might not be overkill here. In any case, I first gave this to a >GM to look at and the response "black wins easily." Not surprising, the >bishop pair vs the pair of knights should favor the bishops. I then told >him that Crafty "statically" evaluates this position as "-.93" which is >the raw score Evaluate() returns here. He said "hmmm... ". And we had >an interesting conversation without concluding whether this is too large, >too small, or "just right." > I think, when adding knowledge to the current evaluator, we should not think like humans: the program has only to know that one position is better than an another. If the score of a position is higher than the score of another position it doesn't matter how big the difference is, since the move choice doesn't change. So, if we see the score "-.93" it says only that one side seems to be winning, but nothing more. The program needs only to know *that* this position is better than others. Ciao Alessandro
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