Computer Chess Club Archives




Subject: Re: Double Null move?

Author: Uri Blass

Date: 13:50:26 07/13/01

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On July 13, 2001 at 14:25:23, Robert Hyatt wrote:

>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

If you search to clearly reduced depth(for example before normal search with
null move pruning to depth d when d>=6 you search without null move to depth
d/2-2) then you may be less than 1% slower.

I believe that it is a good deal to be 1% slower in order to avoid not seeing
simple zunzwangs.

I guess that you may earn 3 elo from not falling in some zunzwangs and lose only
1 elo from being slightly slower.


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