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Subject: Null move window?

Author: Inmann Werner

Date: 05:56:53 06/28/99


I use Null Move now for one year and works fine.
I make the null move and call alpha-beta with (alpha,beta,distance-3).

Now I read, and it seems logical to me, that (beta-1,beta) would be enough. I
tried it and everything slowed down (tree bigger!)... Oops.

I tried to figue out why, and think now, it is because of the hash tables.
During the null move, only beta-1,beta is searched and stuffed in, and so i get
later less "finds" in hash table(the bounds say no for fails). That was, what i
figured out. Surely, this only happens in PV changing, cause there I have a more
open window.
Normally, entrys in hash with null moves should have other hashpositions than if
no null move occured, and therefore the behaviour is strange.

If I make a null move for white I change the hashadress with a special hashcode,
and if it is a black nullmove I use another code. Is this normal?, or do other
programmers do it another way?

Werner



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