Computer Chess Club Archives




Subject: Re: Null-Move: Difference between R = 2 and R = 3 in action

Author: Omid David

Date: 12:42:36 07/15/02

Go up one level in this thread

On July 15, 2002 at 14:42:52, Robert Hyatt wrote:

>On July 15, 2002 at 13:30:54, Gian-Carlo Pascutto wrote:
>>On July 15, 2002 at 13:11:09, Christophe Theron wrote:
>>>Why does double null move prove that null move is a correct search method????
>>>Doing two null moves in a row means going back to standard search (a search not
>>>involving an illegal move like null move is).
>>>I fail to see how it legitimates null move.
>>I think the idea is simply to show that you can nullmove and still
>>have a correct search. (but only with double nullmove, not single)
>I think the discussion is pointless, myself.  Null-move search is _not_
>equlvalent to non-null-move search.  It demonstrably has more errors due to
>reducing the depth on many sub-trees.
>The concept of "correct search" is therefore so abstract as to mean absolutely
>nothing.  double-null eliminates _some_ zugzwang problems, but not _all_.  It
>is obviously impossible to eliminate all of them, particularly when you are
>whacking 6 plies off the tree depth and then drawing conclusiong about the
>resulting sub-trees..
>The only useful definition of "correct search" would be to somehow prove
>that a null-move search to depth=D would produce the _same_ move as a
>non-null-move search to depth=D, for all positions.  This is simply not

Well, all these ideas try to deal with zugzwangs. As I said before IMO the main
null-move deficiency remains the horizon effect. However the gains from
null-move pruning by far exceed the risks.

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