Author: James Robertson
Date: 23:34:09 09/09/99
Go up one level in this thread
On September 10, 1999 at 00:19:37, Robert Hyatt wrote: I store all my mates as bounds, a la Ferret (I think). My program solves the position in 1 second at ply 13 on my P233, 4MB hash table. (I used the EPD string from William's post). 1 -350 0 3 Kh3 2 -370 0 16 Kh3 f2 3 -365 0 51 Kh3 f2 Kg2 4 -360 0 418 Kh2 Kf4 Kg1 Ke4 5> -497 0 872 Kh3 Kf4 Kh2 Kg4 Kg1 Kxh4 5 -497 50 872 Kh3 Kf4 Kh2 Kg4 Kg1 Kxh4 6 -1169 50 1341 Kh3 f2 Kg2 Ke2 Kg3 f1=q 7 -1169 50 1894 Kh3 f2 Kg2 Ke2 Kh2 f1=q Kg3 8 -1176 50 2636 Kh3 f2 Kg2 Ke2 Kh2 f1=q Kg3 Kd3 9 -1246 50 3593 Kh3 f2 Kg2 Ke2 Kh2 f1=q Kg3 Qa1 Kf4 Qxa6 10 -1263 110 12151 Kh3 f2 Kg2 Ke2 Kh1 f1=q+ Kh2 Ke3 Kg3 Qxa6 11 -1326 220 25148 Kh3 f2 Kg2 Ke2 Kh3 f1=q+ Kg3 Qg1+ Kh3 Qg4+ Kh2 Qx h4+ 12 -1331 380 63883 Kh3 f2 Kg2 Ke2 Kh3 f1=q+ Kg3 Qf3+ Kh2 Qg4 Kh1 Qxh 4+ 13 -29988 990 202497 Kh3 f2 Kg2 Ke2 Kh3 Kf3 Kh2 g5 hxg5 f1=q g6 Qg2+ I am surprised a 12 ply search does not see the mate; there might be a bug somewhere? James >Here is an interesting position given to me by Steffen Jakob: > > /p/P5p/7p/7P/4kpK/// w > > +---+---+---+---+---+---+---+---+ > 8 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > 7 | *P| | | | | | | | > +---+---+---+---+---+---+---+---+ > 6 | P | | | | | | *P| | > +---+---+---+---+---+---+---+---+ > 5 | | | | | | | | *P| > +---+---+---+---+---+---+---+---+ > 4 | | | | | | | | P | > +---+---+---+---+---+---+---+---+ > 3 | | | | | *K| *P| K | | > +---+---+---+---+---+---+---+---+ > 2 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > 1 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > a b c d e f g h > > >Obviously black is getting crushed. He has one move, Kh3, which leads to a >mate in 6. Steffen asked me to try this and Crafty found a mate in 4, which >doesn't exist. I spent the entire day debugging this thing and here is what >I found: > >If you recall the discussion here a couple of weeks ago, I reported that I store >absolute mate scores (EXACT scores) in the hash table, and that I adjust them >so that they are always stored as "mate in N from the current position". This >has always worked flawlessly for me, and still does. > >For bounds, I once tried adjusting the bounds as well, but found quirks, and >left them alone. Wrong answer. To fix this mate in 4 problem, I decided to >adjust the bounds as well, but I now set any bound value that is larger than >MATE-300, by reducing it to exactly MATE-300, but still using the "LOWER" >flag to say that this is the lowest value this position could have. For bound >values < -MATE+300, I set them to exactly -MATE+300 and leave the flag as is. > >This position is cute. Because not only is it a mate in 6, but there are >transpositions that lead to mate in 7, mate in 8, and there are shorter (but >non-forced) mates in 4 and 5. And there are stalemates, and positions with >1 legal move, and so forth. > >You ought to find the following variation as one mate in 6: > >Kh3, f2, Kg2, Ke2, Kg3, f1=Q, Kh2, g5, hg, Kf3, g6, Qg2# > >If you find a shorter mate, it is wrong. If you find a longer mate, you >are probably just extending like mad on checks (crafty finds a mate in 8 at >shallow depths (9 plies, 2 secs on my PII/300 notebook), and doesn't find the >mate in 6 until depth 10, 3 seconds. > >It is a good test as the transpositions are real cute with white's king caught >in a tiny box, but with several different moves that triangulate and transpose >into other variations... > >If you get it right, you have either handled the bounds right, or else you are >very lucky. IE Crafty 16.17 gets this dead right. But if I disable the eval, >it goes bananas, yet the eval is not important when mate is possible. > >Have fun... > >I did... :)
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