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Subject: Re: Verified Null-moving

Author: martin fierz

Date: 05:38:46 08/12/04

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On August 12, 2004 at 07:12:08, Tord Romstad wrote:

>On August 12, 2004 at 06:40:48, Ross Boyd wrote:
>
>>Be careful with R=3. It has the potential to make your engine go blind. I lost
>>~50 (!!) elo when using pure R=3 in TRACE. I ran the experiment again two days
>>ago and it confirmed my previous findings. Currently, pure R=2 works best for
>>me... fewer OTB blunders.
>
>Like virtually everything else in computer chess, this is something which
>varies a lot between different engines.  In my engine pure R=3 works
>*much* better than R=2, and slighly bettter than the classic adaptive
>null move pruning technique.  Verified null move pruning also didn't
>work for me.  The only improvement I have found over pure R=3 is a scheme
>were I occasionally use R=2 in positions where horizon effect problems
>are likely to be a problem (I use the eval to make the decision).
>
>Part of the reason that R=3 is best for me could be that my engine doesn't
>use null moves as much as most other engines.  I only do a null move search
>when I am reasonably sure of a fail-high, but not quite sure enough to
>prune the whole subtree without search.  Null move at all nodes more than
>doubles my node count, and does not increase the accuracy of my search
>noticably.
>
>Tord

hi tord,

i'm intrigued by your last sentence - that null move at all nodes more than
doubles your node count! i wonder how this is possible at all? why? if i
understand what you write you have an oracle which can tell you whether you
should do a null-move search at a given node or not.

int alphabeta(....)



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