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Subject: Re: Question about aspiration search

Author: Robert Hyatt

Date: 17:18:23 03/24/04

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On March 24, 2004 at 11:17:48, Fabien Letouzey wrote:

>On March 24, 2004 at 10:54:31, Robert Hyatt wrote:
>
>>On March 24, 2004 at 07:21:04, Fabien Letouzey wrote:
>>
>>>On March 23, 2004 at 17:17:01, Russell Reagan wrote:
>>>
>>>>On March 23, 2004 at 16:18:24, Robert Hyatt wrote:
>>>>
>>>>>Hashing can cause odd things.
>>>>>
>>>>>For example, you ponder for an abnormally long time and finish (say) a 16 ply
>>>>>search.  As you searched position X at ply=1 (not depth = 1  but ply =1...) you
>>>>>get a "fail low" and store (say) score <= XXX, draft=15.
>>>>>
>>>>>Your opponent makes a different move and you start over.  When you reach
>>>>>position X, you get a hash hit and you "fail low" because of it, bit when you
>>>>>re-search, you can't use that old fail low hash entry and you are not searching
>>>>>deeply enough to see the 16 ply problem with the move, so you get a screwy
>>>>>score.
>>>>>
>>>>>There is no solution to this...  except drop hashing...
>>>>
>>>>To be more precise, you don't have to "drop hashing" completely to avoid this.
>>>>For example, you could still use the hash table only for move ordering and avoid
>>>>the search instability. Of course, it is less effective then. Pick your poison
>>>>:)
>>>
>>>I do exactly that at PV nodes in Fruit, for exactly that reason.
>>>Please stop having exactly the same ideas as I do ;)
>>>
>>>Fabien.
>>
>>
>>That doesn't solve the problem at all.  A non-PV move can have a fail-high
>>stored in the table.  You fail high on the move then fail low when you can't
>>resolve it...
>
>Sorry I was talking about depth/draft inconsistencies.
>I don't use aspiration at all.
>
>Fabien.


So was I.  You have only solved the problem along the PV.  It _still_ exists
along non-PV moves just as I explained...

this has nothing to do with aspiration issues...



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