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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.
>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
>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.

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