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Subject: Re: Repeatability (questions for Omid)

Author: Uri Blass

Date: 05:57:50 12/19/02

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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:
>>>>
>>>>><snip>
>>>>>>>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.
>>>
>>>Martin
>>
>>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.
>>
>>Uri
>
>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
>research.

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.

Uri



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