Author: Uri Blass
Date: 06:59:10 12/15/05
Go up one level in this thread
On December 15, 2005 at 08:56:14, Richard Pijl wrote: >On December 15, 2005 at 05:59:21, Gerd Isenberg wrote: > >>Hi, >> >>recently there was the question about a knight-distance formula. >>Mungjong pointed out the idea with the 0x88 square difference and a lookup, >>while Uri mentioned the edge-cases which require some special handling. >> >>I still have my precalculated 64*64 array with packed distance, taxi-distance, >>knight-distance and this udr-value (unique distance relation). >> > >I'm not sure what you can do with the knight-distance. >The obvious case (to check whether a passed pawn can be stopped by the knight) >is obviously not very useful, as there are plenty of cases where the knight (by >means of an intermediate check) can 'win' a move. Of course the knight can win a move but you still may detect unstoppable pawn if the knight need to win 2 moves to stop the pawn or cases that the knight cannot win a move thanks to calculation of the distance to the opponent king. Besides, in most cases the >'stopping' capability of the knight is more restricted by pawn and king >positions than anything else anyway. Of course it is clear that distance function cannot detect all the cases when pawns are unstoppable but only part of the cases. finally, you should also consider >alternative stopping fields like the second rank, as sometimes it is possible to >reach a stopping field other than the promotion square. of course but I do not think that checking distance to some squares is expensive. I do nothing about it and I did not see Movei lose many games because of not detecting unstoppable passed pawns. I suspect that the main advantage is simply being able to prune lines and search faster but the advantage is limited and middle game evaluation is more important. Rybka that is probably the best program does not detect it by evaluation as the following analysis prove(it shows a score of +12 inspite of the fact that even without seeing that black promote with check black queen first) Note that Movei has big problem in this type of positions today and it's search is very unstable and it needs depth 10 to see that white is losing. New game, [D]k6N/8/8/p7/8/6PP/8/7K w - - 0 1 Analysis by Rybka 1.0 Beta 32-bit: 1.Nf7 +- (12.21) Depth: 3 00:00:00 1.Nf7 +- (11.44) Depth: 4 00:00:00 1.Nf7 Kb7 +- (3.95) Depth: 5 00:00:00 1.Nf7 a4 2.g4 -+ (-5.22) Depth: 6 00:00:00 5kN 1.Nf7 a4 2.Kh2 a3 -+ (-5.22) Depth: 7 00:00:00 11kN 1.Nf7 a4 2.Kh2 a3 3.Ne5 -+ (-5.28) Depth: 8 00:00:00 13kN 1.Nf7 a4 2.Kh2 a3 3.Ne5 a2 4.Nc4 -+ (-5.28) Depth: 9 00:00:00 16kN 1.Nf7 a4 2.Kh2 a3 3.Ne5 a2 4.Nc4 a1Q -+ (-5.28) Depth: 10 00:00:00 18kN 1.Nf7 a4 2.Kh2 a3 3.Ne5 a2 4.Nc4 a1Q 5.Ne3 -+ (-5.28) Depth: 11 00:00:00 23kN 1.Nf7 a4 2.Kh2 a3 3.Ne5 a2 4.Nc4 a1Q 5.Ne3 Qa2+ -+ (-5.28) Depth: 12 00:00:01 31kN 1.Nf7 a4 2.Kh2 a3 3.Ne5 a2 4.Nc4 a1Q 5.Ne3 Qa2+ -+ (-5.28) Depth: 13 00:00:01 40kN 1.Nf7 a4 2.Kh2 a3 3.Ne5 a2 4.Nc4 a1Q 5.Ne3 Qa2+ -+ (-5.28) Depth: 14 00:00:01 50kN 1.Nf7 a4 2.Kh2 a3 3.Ne5 a2 4.Nc4 a1Q 5.Ne3 Qa2+ -+ (-5.28) Depth: 15 00:00:02 61kN 1.Nf7 a4 2.Kh2 a3 3.Ne5 a2 4.Nc4 a1Q 5.Ne3 Qa2+ -+ (-5.28) Depth: 16 00:00:02 77kN 1.Nf7 a4 2.Kh2 a3 3.Ne5 a2 4.Nc4 a1Q 5.Ne3 Qa2+ -+ (-5.28) Depth: 17 00:00:02 99kN 1.Nf7 a4 2.Kh2 a3 3.Ne5 a2 4.Nc4 a1Q 5.Ne3 Qa2+ -+ (-5.28) Depth: 18 00:00:02 124kN (, 15.12.2005) Another position when Movei is better in finding black's win but rybka is slower in finding score above draw. [D]k6N/8/8/p7/8/6PP/r6R/7K b - - 0 1 Analysis by Rybka 1.0 Beta 32-bit: 1...Ra1+ = (0.00) Depth: 3 00:00:00 1...Ra1+ 2.Kg2 Ra2+ 3.Kg1 = (0.00) Depth: 4 00:00:00 1...Ra1+ 2.Kg2 Ra2+ 3.Kg1 Ra1+ 4.Kf2 = (0.00) Depth: 5 00:00:00 1...Ra1+ 2.Kg2 Ra2+ 3.Kg1 Ra1+ 4.Kf2 Ra2+ 5.Kg1 Ra1+ 6.Kf2 = (0.00) Depth: 6 00:00:00 1...Ra1+ 2.Kg2 Ra2+ 3.Kg1 Ra1+ 4.Kf2 Ra2+ 5.Kg1 Ra1+ 6.Kf2 = (0.00) Depth: 7 00:00:00 1...Ra1+ 2.Kg2 Ra2+ 3.Kg1 Ra1+ 4.Kf2 Ra2+ 5.Kg1 Ra1+ 6.Kf2 = (0.00) Depth: 8 00:00:00 1kN 1...Ra1+ 2.Kg2 Ra2+ 3.Kg1 Ra1+ 4.Kf2 Ra2+ 5.Kg1 Ra1+ 6.Kf2 = (0.00) Depth: 9 00:00:00 1kN 1...Ra1+ 2.Kg2 Ra2+ 3.Kg1 Ra1+ 4.Kf2 Ra2+ 5.Kg1 Ra1+ 6.Kf2 = (0.00) Depth: 10 00:00:00 2kN 1...Ra1+ 2.Kg2 Ra2+ 3.Kg1 Ra1+ 4.Kf2 Ra2+ 5.Kg1 Ra1+ 6.Kf2 = (0.00) Depth: 11 00:00:00 3kN 1...Ra1+ 2.Kg2 Ra2+ 3.Kg1 Ra1+ 4.Kf2 Ra2+ 5.Kg1 Ra1+ 6.Kf2 = (0.00) Depth: 12 00:00:00 5kN 1...Rxh2+ 2.Kxh2 a4 3.Nf7 a3 4.Ne5 a2 5.Nc4 a1Q 6.Ne3 -+ (-5.28) Depth: 12 00:00:00 39kN 1...Rxh2+ 2.Kxh2 a4 3.Nf7 a3 4.Ne5 a2 5.Nc4 a1Q 6.Ne3 -+ (-5.28) Depth: 13 00:00:01 46kN 1...Rxh2+ 2.Kxh2 a4 3.Nf7 a3 4.Ne5 a2 5.Nc4 a1Q 6.Ne3 -+ (-5.28) Depth: 14 00:00:01 56kN 1...Rxh2+ 2.Kxh2 a4 3.Nf7 a3 4.Ne5 a2 5.Nc4 a1Q 6.Ne3 -+ (-5.28) Depth: 15 00:00:02 71kN 1...Rxh2+ 2.Kxh2 a4 3.Nf7 a3 4.Ne5 a2 5.Nc4 a1Q 6.Ne3 -+ (-5.28) Depth: 16 00:00:02 90kN (, 15.12.2005) Uri
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