Author: Frederic Friedel
Date: 03:18:04 02/04/00
Go up one level in this thread
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). 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)
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.