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Subject: Re: Double Null move?

Author: Robert Hyatt

Date: 11:25:23 07/13/01

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On July 13, 2001 at 12:28:01, Steve Maughan wrote:

>I'm thinking of implementing double null move in my program.  Now as far as I
>know the most conventional way is to do the normal null move search and if there
>is a cutoff follow it with a normal search at reduced depth to confirm no
>zugwag.  However I do remember that someone here (Vincent?) outlined a different
>way of doing double null move.  Is there another way?  If there is, what are the
>pros and cons of each?

That's the gist of it.  If the position is a zugzwang position, the second
null-move search will fail high, which will cause the first to fail low and
you don't run into the zug problem.

The downside is the cost.  The second null will fail low most of the time and
just generate wasted nodes.

The other downside is that not all null-positions are zugzwang problems.  In
fact, most null-move problems are caused by the R-value which bring the horizon
too close to spot a tactical threat.  Double null won't find any of those...

So you expend quite a bit of effort, to eliminate one small part of the total

That's why I don't do it myself....

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