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Subject: Re: Verified Null-moving

Author: Tord Romstad

Date: 04:12:08 08/12/04

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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




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