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Subject: Re: new thoughts on verified null move

Author: Omid David Tabibi

Date: 09:52:21 11/23/02

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On November 23, 2002 at 11:37:25, Martin Giepmans wrote:

>On November 23, 2002 at 08:48:36, Omid David Tabibi wrote:
>
>>On November 23, 2002 at 08:45:00, Uri Blass wrote:
>>
>>>On November 23, 2002 at 08:11:37, scott farrell wrote:
>>>
>>>>Just after other people's thoughts.
>>>>
>>>>I think Omid's work overlooked the adapative null move searching many of us do,
>>>>ie. transitioning from r=3 to r=2.
>>>>
>>>>I think adaptive null move tries to GUESS where to use r=2 to reduce the errors
>>>>that R=3 makes. I guess it depends on how often this GUESS is correct, the cost
>>>>of the verification search, and how long it takes the adaptive searching to
>>>>catch the error at the next ply.
>>>>
>>>>Has anyone looked at setting the verification search to reduced depth of 2
>>>>(rather than 1)? obviously to reduce the cost of the verification search.
>>>
>>>Omid checked it but you also reduce the gain.
>>>
>>>I think that I will look for good rules when to do the verification search so
>>>the cost will be significantly smaller but the gain is going to be the same in
>>>at least 99% of the cases.
>>>
>>
>>I'm currently working on other variations. The initial results are promising.
>>
>>>Uri
>
>I have done some tests with your method at greater depths.
>At depth 12 vrfd R=3 still had an overhead (in terms of treesize) of about
>25% compared to pure R=3.

Of course verified R=3 will *always* construct a larger tree than standard R=3.
However, starting from a certain depth, it will always construct a smaller tree
than standard R=2.

Take note, that while verified R=3 constructs a slightly larger tree than
standard R=3, it has a superior tactical strength to even R=2 !


>
>(my engine uses a simple Q-search that shouldn't give problems here)
>
>So the question is if your expectation that the treesize of R=3 and vrfd R=3
>converge at greater depths (> 11) really holds.
>
>Needs more testing, I think.
>
>Another point:
>I would expect that vrfd R=3 becomes less safe at greater depths.
>The subtrees in which you don't verify nullmove (after the verification) become
>deeper and I see no reason - on logical grounds - why this shouldn't give safety
>problems.
>Even if R=3 and vrfd R=3 converge in terms of treesize, the safety (or rather
>the lack of it) might also converge ...
>

None will converge.
However, the deeper you go, the smaller will be the difference in tree size, and
the greater the difference in tactical strength.


>In any case, thanks for sharing.
>
>Martin



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