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Subject: Re: Verified Null-moving

Author: Ross Boyd

Date: 03:40:48 08/12/04

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On August 12, 2004 at 00:21:42, Tor Lattimore wrote:

>I have been fiddling arround with my nullmove pruning lately. I have tried both
>R=2, R=3 and R=3 with verifications.
>
>Average ply on WAC, 1 second a move P IV, 512 MB ram:
>R=2      9.5
>R=3      10.5
>R=3 with verification      10.2
>
>However R=3 had a terrible success rate (135 or so), R=2 got 147 and R=3 with
>verification got 143. What do other people use here? and what sort of
>improvments do you get? The extra ply may be worth the puzzle sacrifice, but i'm
>not convinced i'm really *getting* the extra ply.
>Thanks
>Tor

Hi Tor,

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. Mind you, the test machine was a 450Mhz P3 so that
would skew the results in favour of R=2... and I don't test at slow time
controls because life is too short. :-)

You could try an adaptive approach which is R=3 by default and R=2 when
remaining depth is < 6 ply.... or something like that.

As always, YMMV...

It obviously depends on a whole lot of factors eg. do you use futility pruning,
delta pruning, SEE pruning, hash pruning? Do you try quiet checks in qsearch if
captures don't return a score above alpha? All these things will interact with
the null reduction factor...

I believe the engines which perform okay with R=3 are compensating by, for
example, not qsearch/futility pruning moves which dramatically reduce king
safety or affect other positional factors. That's just a theory.

I guess all you can do is test, test and test... and keep what works... ditch
what doesn't. :-)

Best regards,

Ross






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