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Subject: Re: Question about aspiration search

Author: Fabien Letouzey

Date: 04:21:04 03/24/04

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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.




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