Author: Gareth McCaughan
Date: 11:47:48 10/07/01
Go up one level in this thread
Robert Hyatt wrote: [Slater Wold mentioned the following position and asked how long programs take to see that Qxd4 draws:] >>>> [D]8/1kbQ2NK/4p2p/8/1p1p1P2/8/4q3/8 w - - 0 1 >>>> >>>> Solution is Qxd4! and the game draws. [I reported:] >>> Crafty 18.11, Athlon 1GHz, takes about 15 1/2 hours >>> to switch from Nxe6 to Qxd4. It doesn't think it's >>> drawing (eval is about -2.6). >>> >>> At the moment (nearly 60 hours in) it's working on >>> ply 20 and doesn't have an eval or a PV yet. >>> The PV at the end of ply 19 is: >>> >>> 1. Qxd4 Qc2+ 2. Kxh6 b3 3. Nxe6 b2 >>> 4. Nc5+ Kc6 5. Qd7+ Kb6 6. Na4+ Qxa4 >>> 7. Qxa4 b1=Q 8. Qd4+ Kc6 9. Qc4+ Kd6 >>> 10. Qd4+ Ke6 11. Qc4+ Kd7 12. Qf7+ >>> Kc8 13. Qg8+ Bd8 14. Qe6+ Kc7 15. Qe5+ >>> Kd7 16. Qd5+ Ke7 17. f5 [Uri Blass said:] >> The position after 7...b1Q should be evaluated as something >> close to draw because queen and bishop usually does not win >> against queen and here black has queen and bishop against >> queen and pawn. [Bob:] > Nope. Never included all the special cases, just the ones that > I have seen such as KR+minor + KR or KR+P. Lots of KQB vs KQP > are winnable. enough that just saying "draw" would lead to > embarassing results. This problem will become moot in another > couple of years as more 6=piece EGTBs are done. I think it is > dangerous to call KR vs KN a draw, because some are winnable, > and I watched a game vs some computer on ICC last week where > this came up. Crafty was in a KRP vs KBN ending and the opponent > played BxP with an eval of 0.00, and crafty responded RxB with > a score of mate in something. Apparently the opponent had > that particular score hard-coded, and if there are exceptions, > that becomes embarassing at a critical moment... Sure. But then, playing Nxe6 instead of Qxd4 in Slater's position because you think the position after Qxd4 is -2.6 is also embarrassing. Obviously it would be dangerous to tell Crafty (or any other program) that KQB v KQP endings are all drawn (i.e., score of 0 and stop searching), but if you have the choice between being wrong 70% of the time by saying -2.6 or being wrong 30% of the time by saying -0.5 then the latter is better. (All the numbers in the previous sentence were pulled out of a hat and could be badly wrong, but the point I'm making is fairly stable under such perturbations.) -- g
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