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Subject: Re: Nullmove: when to avoid it? Why not when depth=1?

Author: Robert Hyatt

Date: 19:06:14 03/02/01

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On March 02, 2001 at 16:01:21, Ernst A. Heinz wrote:

>Hi Severi,
>>>>>I can save bunches of nodes by not nullmoving on the last ply before
>>>>>qsearch. So if depthleft == 1 ply then not nullmoving reduces
>>>>>for me the number of nodes considerably.
>>>>Interesting idea, I'll give it a try in my engine.
>>>Try it severi!
>>>I have observed the same thing. I don't do nullmove
>>>unless depth > 1. I think it makes sense.
>>Why does it make sense? I have not yet tried it but I don't understand why
>>should it be better? Do you have any opinions? I allways want to understand the
>>features I put into my engine and I don't get this one...
>Easy -- the relative cost of a depth-reduced null-move search
>at frontier nodes (with a remaining depth of 1 ply) is just
>too high. Most normal searches from there also go straight into
>quiescence mode and the gain of null-move cutoffs does not seem
>to outweigh the added null-move search effort.

I tried this for a quick test.  It is actually slower overall than doing
null-move everywhere.  A couple of positions were faster.  But more were
slower.  I ran all the kopec positions...

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