Author: Robert Hyatt
Date: 05:34:25 02/04/00
Go up one level in this thread
On February 04, 2000 at 07:02:41, Ulrich Tuerke wrote: >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 >> or just turn it off close to the root if one side has a rook or less, which works wonders for me. > >>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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