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Subject: Re: How do hash tables help move ordering? (Fail Low)?

Author: Robert Hyatt

Date: 06:11:47 09/21/98

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On September 21, 1998 at 00:12:04, David Eppstein wrote:

>On September 20, 1998 at 20:58:08, Robert Hyatt wrote:
>>On September 20, 1998 at 17:49:17, Inmann Werner wrote:
>>>Whats the thing with the fail low?
>>>Why can I not use the Hash table for move ordering in this case?
>>>(I do now!)
>>You can't...  if you fail low, all you know is that for every move at that
>>ply, the opponent has a move that "refutes" it.  You have *no* idea about which
>>move is best, which is worst, which are "in the middle".
>
>All true.  But I don't see any harm in using a fail low hash node for move
>ordering anyway...the move ordering information is not useful but also not
>harmful...because at a fail low node, it doesn't matter what order you search
>the children.
>
>The one thing you really have to be careful of with fail-lows, is that if you
>ever get a fail-low at the root, don't ever use the result of that search to
>tell you which move to actually make.


How can you use a fail-low hash table entry for move ordering?  You have *no*
clue which move is best, you only know that all are bad...



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