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Subject: Re: Repeatability (questions for Omid)

Author: Martin Giepmans

Date: 06:32:40 12/19/02

Go up one level in this thread

On December 19, 2002 at 08:57:50, Uri Blass wrote:

>On December 19, 2002 at 08:47:02, Martin Giepmans wrote:
>>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.
>If it only use null move on ply 2, but programs do not do it.
>>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
>I agree that there is difference but not because of not symmetric searching but
>because it is possible that the research gives you better information at the
>cost of time.

It's not so easy to figure this out, but my hunch is that verification of
nullmove without research is in fact incorrect.
What is verified in this case? Nullmove pruning? Not exactly ...

Of course I know that many things that we use in our programs are not
100% correct. "search instabilities", hmm, I don't like them, do you?



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