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Subject: Re: new thoughts on verified null move

Author: Omid David Tabibi

Date: 10:42:06 11/23/02

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On November 23, 2002 at 13:29:38, Martin Giepmans wrote:

>On November 23, 2002 at 12:52:21, Omid David Tabibi wrote:
>
>>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.
>
>That is what you hope. And hope is a good thing, for sure :)
>

That's what I hope? No, actually I would be happier if the tree size of vrfd R=3
and std R=3 would converge! But that is impossible, since verified R=3 has the
verification overhead.


>But how do you know? In your article there are no results for depths>11.
>

Look at Figure 4. The deeper you go, the larger becomes the difference between
the tree size of vrfd R=3 and std R=2.


>>However, the deeper you go, the smaller will be the difference in tree size,  and the greater the difference in tactical strength.
>>
>Again, how do you know?
>

The "backbone" of verified null move pruning is R=3. So it is natural that the
deeper you go, the size of the tree will be closer to standard R=3 than to
standard R=2 (again see Figure 4).


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



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