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

Author: Ernst A. Heinz

Date: 16:23:41 03/02/01

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>>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.
>
>Yes, this seems to be the case - has this been tested in even higher remaining
>depths (2,3...)?. Maybe in some situations your could turn null moves off at
>pre-frontier nodes also? After all, this would lead straight to qsearch? Maybe
>limiting null moves to levels where remaining depth after the depth reduction is
>at least 1 to allow any kind of move for opponent. I'll have to test this.
>
>I tested the version that disables when d==1 and got 0-10% reduction in the node
>count (only in a couple of positions...) so this seems to be a very good idea.

Yes, almost everybody seems to disable null moves at frontier
nodes -- including "DarkThought"!

Disabling null moves at pre-frontier nodes does not look so
clear-cut because there most normal searches do _not_ hit the
quiescence mode directly. Hence, the null-move overhead still
seems to pay off at pre-frontier nodes.

=Ernst=



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