Author: Robert Hyatt
Date: 07:46:55 10/29/01
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On October 28, 2001 at 06:37:59, Ferdinand S. Mosca wrote: > >[D]3k4/8/1p3K2/8/4P1p1/6P1/7P/8 b - - 0 91 >A position from a game (Yace 0.99.56-Crafty 18.12) in a slow P3-550mhz machine >at 75 minutes per side with some 5 men Nalimov TB's. > >Crafty could have avoided this position and draws some moves back, but it >follows in this direction. Is this not caused by the evaluate winner() function? No. EvaluateWinner() is generally correct. IE if white has a king and bishop + wrong rook pawn, and black can get to the promotion square, then white can't possibly win and EvaluateWinner() will report this. If black has a couple of pawns or a pawn and piece, then EvaluateWinner() will look at _his_ chances using rules similar to the wrong rook pawn rules. In this position, EvaluateWinners() returns a 11 result (either can win). EvaluateWinner() is designed to catch positions like KRB vs KRPP. The KRB has no chance of winning. KRPP _can_ win. EvaluateWinner() returns a result that indicates that which tells the Search to avoid such positions with the KRB and accept them (if the pawns are advanced enough) for the KRPP side. In KRB vs KRPP the score will _never_ be positive. It will either be zero, if the pawns are not advanced very far, or less than zero if the black pawns are getting advanced enough to be a problem. But _never_ greater than zero since white has no chances. >BTW Bob, what are the bases that this function can tell more correctly that one >is winning/losing/drawing in a given position? Will somebody let Crafty analyze >this position in a faster machine? See above. A single minor piece is not enough to win. IE KRB or KRN vs KR. KB or KN vs K. Wrong bishop + rookpawn. Etc. It doesn't try to detect every case. If it is sure, it will indicate that side can't win. If it is not sure, it assumes it can. > >How your favorite engines react to this? The target is for black to accept that >white is winning (this is perhaps a mate in more than 45 moves) in a reasonable >period of time considering that we are in an ending stage. > >Regards, Cruuent version thinks white is winning after 3 seconds on a PIII/750 laptop. >Dinan
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