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Subject: Re: Repeatability (questions for Omid)

Author: Martin Giepmans

Date: 05:47:02 12/19/02

Go up one level in this thread

On December 19, 2002 at 01:46:01, Uri Blass wrote:

>On December 18, 2002 at 22:19:24, Martin Giepmans wrote:
>>On December 18, 2002 at 21:51:20, Omid David Tabibi wrote:
>>>On December 18, 2002 at 21:44:09, Martin Giepmans wrote:
>>>>>>I don't understand what you are trying to say.
>>>>>>Without a research (if the verification search with reduced depth doesn't
>>>>>>give a cutoff) verification search would be pointless.
>>>>>The verification search goes deeper than the null-move search, so it might find
>>>>>tactical errors overlooked by the null-move search, and correct them (without
>>>>>any need for a re-search).
>>>>No need for a research ??????????
>>>>It's late, I guess we are talking about two different things?
>>>No we aren't :-)
>>>When we have a fail-high report, we simply reduce the depth, and continue a
>>>regular search, as if nothing has happened. Because this regular search (which
>>>can be called verification search) goes deeper, it might find out threats beyond
>>>null-move search's horizon. In that case, you would get the correct result even
>>>if you don't do a re-search!
>>Yes, we _were_ talking about 2 different things :)
>>My thing is verification search, yours is what I would call "de-extension".
>>One difference is that de-extensions are symmetrical (you reduce depth for
>>both colors) while (standard) verification search is essentially asymmetrical.
>>I think it's possible that at least some of the readers of your article
>>got confused here and implemented something in their programs that you
>>didn't intend. Perhaps that explains why in many cases your method didn't
>>seem to work.
>I do not understand
>How can you reduce depth for only one color?
>There is only one varaible with the name depth in my program.

That's right, but the effect is asymmetrical.
It's the same with nullmove.
Suppose a program has white and only uses nullmove on ply 2.
The effect is that it may overlook a good continuation for white, but
_not_ for black. Nullmove pruning is (in effect) asymmetrical.

Standard verification search (always research) is also asymmetrical.
If you leave out the research it becomes symmetrical: it may
overlook good continuations for _both_ sides.

I think there is a fundamental difference between vs with and without


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