Author: Ulrich Tuerke
Date: 04:02:41 02/04/00
Go up one level in this thread
On February 04, 2000 at 06:18:04, Frederic Friedel wrote: >On February 04, 2000 at 05:33:53, Georg Langrath wrote: > >>About this position. Fritz 5.32 can't find this mate in three. Fritz 6 can find >>it in time mode, but not in analyze mode. In my opinion that is an ugly bug. >> >>Then somebody says that it is a null-move problem. Then no more with that. When >>it is a null-move problem is seems as it is acceptable in the world of >>chesscomputers and no more to add. In my opinion it is still very ugly that a >>modern chesscomputer can't find a mate in three. >> >>I think that it is done before, but can somebody explain this mystical null-move >>so also an amateur understands? I think it is some kind of holy magic power that >>you must not heckle. > >Null move is a pruning technique based on the assumption that in certain parts >of the search you can ignore moves that threaten nothing. This gives you great >speed-ups because the program doesn't spend inordinate amounts of time checking >really silly lines. But it does lead to blindness in some zugzwang positions. >99% of these are studies or artificial problem positions. I can't remember >encountering a fatal zugzwang in a normal tournament game (though I'm sure CCC >forum members will immediately supply examples). > >In order to solve positions like the one you gave you must switch off >"Selectivity" (click the engine or press F3 to do so). That effectively switches >off the null-move pruning. Remember to switch it back on afterwards. Here is the >log of the search with selectivity=0. The mate is found in 00:00:00 after a >four-ply search (six-ply extensions). > Frederic, I should strongly suggest the program itself to switch off null move as soon as either side has only one minor piece or less. Regards, Uli > >New position >[D]3n4/8/pppN4/k7/2P5/1K6/P7/8 w - - 0 1 > >Analysis by Fritz 6: > >1.c5 > µ (-1.34) depth: 1/3 00:00:00 >1.c5 > µ (-1.34) depth: 1/3 00:00:00 >1.a3 > µ (-1.09) depth: 1/3 00:00:00 >1.a3 > ³ (-0.66) depth: 1/3 00:00:00 >1.a3 c5 > ³ (-0.66) depth: 2/4 00:00:00 >1.c5 > ³ (-0.59) depth: 2/5 00:00:00 >1.c5 b5 > ³ (-0.41) depth: 2/5 00:00:00 >1.c5 b5 2.a3 > ³ (-0.44) depth: 3/5 00:00:00 >1.c5! > +- (3.19) depth: 4/6 00:00:00 >1.c5! b5 2.a3 Ne6 > +- (#3) depth: 4/6 00:00:00 > >(Friedel, Hamburg 04.02.2000)
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