Author: Dann Corbit
Date: 13:40:01 04/17/02
Go up one level in this thread
On April 17, 2002 at 16:32:47, Uri Blass wrote: >On April 17, 2002 at 16:09:27, Dann Corbit wrote: > >>On April 17, 2002 at 15:43:23, Jesus de la Villa wrote: >> >>> >>>Have someone defined the general rule(s) where null move >>>is unable to find simple combinations?, and if so, which >>>are those rules ? >>> >>>"Obviusly" is more expensive to check it than to not >>>use Null Move. >> >>There are times you simply must turn null move off or disasters will happen. >> >>When the board gets sparse, turn it off. >> >>If you are in check, turn it off. >> >>If you are already searching with null move, additional null move pruning [for >>subsequent plies] is questionable. >> >>If you see a checkmate threat during the null move search, turn it off or >>extend. >> >>Null move will not remove the ability to find simple combinations. It only >>delays it. But it might delay it enough that you will not find it in a >>reasonable time. > >Null move may removes the ability to find simple combinations when zunzwang is >involved. > >It happens to a lot of programs that do not use zunzwang detection(I think that >crafty is one of them and at least it was the case in the latest version that I >checked). It only reduces the depth of the search. So (for instance) a tactic that might take 7 ply to find with a full-width search may take a 9 or 10 ply search to find with null move turned on (depending on the value for R). I don't see how it can completely remove the tactic from ever being seen unless the implementation of null move is broken.
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