Author: Serge Desmarais
Date: 22:03:13 09/28/98
Go up one level in this thread
It is interesting, what you say about the bishop being stronger than the knight when there are pawns on both wings. J.R. Capablanca says just the same in discussing the respective merits of the bishops and knights. (in Chess Fundamentals). He also says that the bishop's advantage is even greater when the pawn masses facing each others are not symetric (e.g. White has 3 pawns on the Q-side and 2 on the K-side while for black it is the reverse). He shows several simple positions, saying that in a dyssymetrical position, it would be tough for the knight to draw. Serge Desmarais 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 have three scoring terms that are producing this -1 pawn advantage for >black here: the bishop pair bonus is .25 (1/4 pawn). The bishops get >a bigger bonus for "mobility" than the knights, and these bishops are >monsters, having almost an open board to roam around, and then my new >"bishops are better than knights in endings with pawns on both sides of >the board" which is .3, but since there are two bishops, this adds up to >.6 > >Any comments on this position? There are a total of 5 of these >interesting positions in the journal article. One with single B vs >N: > > +---+---+---+---+---+---+---+---+ > 8 | | | | | | | *K| | > +---+---+---+---+---+---+---+---+ > 7 | *P| | | | *B| *P| *P| | > +---+---+---+---+---+---+---+---+ > 6 | | | | | *P| | | *P| > +---+---+---+---+---+---+---+---+ > 5 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > 4 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > 3 | | | | | P | N | | P | > +---+---+---+---+---+---+---+---+ > 2 | P | | | | | P | P | | > +---+---+---+---+---+---+---+---+ > 1 | | | | | | | K | | > +---+---+---+---+---+---+---+---+ > a b c d e f g h > >fen: 6k/p3bpp/4p2p///4PN1P/P4PP/6K/ w - - > >score: -.22 > >one with B+R vs N+R (testing the hypothesis that B+R is better than >N+R: > > +---+---+---+---+---+---+---+---+ > 8 | | | | | | | *K| | > +---+---+---+---+---+---+---+---+ > 7 | *P| | *R| | *B| *P| *P| | > +---+---+---+---+---+---+---+---+ > 6 | | | | | *P| | | *P| > +---+---+---+---+---+---+---+---+ > 5 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > 4 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > 3 | | | | | P | N | | P | > +---+---+---+---+---+---+---+---+ > 2 | P | | | R | | P | P | | > +---+---+---+---+---+---+---+---+ > 1 | | | | | | | K | | > +---+---+---+---+---+---+---+---+ > a b c d e f g h > >fen:6k/p1r1bpp/4p2p///4PN1P/P2R1PP/6K/ w - - > >score: -.19 > >(I don't recognize B+R as better. I used to, but didn't like the >result, because with pawns on one side of the board, often the knight >seemed to actually help more than the bishop because the bishop is >locked on one color.) > >Then B+Q vs N+Q, testing the hypothesis that N+Q is better than >B+Q (again, I don't recognize this either, yet). > > +---+---+---+---+---+---+---+---+ > 8 | | | | | | | *K| | > +---+---+---+---+---+---+---+---+ > 7 | *P| | *Q| | *B| *P| *P| | > +---+---+---+---+---+---+---+---+ > 6 | | | | | *P| | | *P| > +---+---+---+---+---+---+---+---+ > 5 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > 4 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > 3 | | | | | P | N | | P | > +---+---+---+---+---+---+---+---+ > 2 | P | | | Q | | P | P | | > +---+---+---+---+---+---+---+---+ > 1 | | | | | | | K | | > +---+---+---+---+---+---+---+---+ > a b c d e f g h > >fen: 6k/p1q1bpp/4p2p///4PN1P/P2Q1PP/6K/ w - - > >score: -.19 > >and finally a B+B vs B+N: > > +---+---+---+---+---+---+---+---+ > 8 | | | | | | | *K| | > +---+---+---+---+---+---+---+---+ > 7 | *P| *B| | | *B| *P| *P| | > +---+---+---+---+---+---+---+---+ > 6 | | | | | *P| | | *P| > +---+---+---+---+---+---+---+---+ > 5 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > 4 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > 3 | | | | | P | N | | P | > +---+---+---+---+---+---+---+---+ > 2 | P | B | | | | P | P | | > +---+---+---+---+---+---+---+---+ > 1 | | | | | | | K | | > +---+---+---+---+---+---+---+---+ > a b c d e f g h > >fen: 6k/pb2bpp1/4p2p///4PN1P/PB3PP/6K/ w - - > >score: -.69 > >(all scores are from Crafty, no search, just a call to the >Evaluate() procedure with the given position set up... > >Comments welcome... Bob
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