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

Author: Inmann Werner

Date: 14:25:38 09/21/98

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On September 20, 1998 at 20:58:08, Robert Hyatt wrote:

>On September 20, 1998 at 17:49:17, Inmann Werner wrote:
>
>>On September 20, 1998 at 17:30:31, Robert Hyatt wrote:
>>
>>>On September 20, 1998 at 14:21:15, John Coffey wrote:
>>>
>>>>I think that the subject says it all.
>>>>
>>>>John Coffey
>>>
>>>
>>>Yes.  You store the best move when you store a position, assuming you
>>>have a best move (you don't if you searched all moves and failed low,
>>>of course.)  You should try this move first each time you encounter this
>>>position...
>>
>>Whats the thing with the fail low?
>>Why can I not use the Hash table for move ordering in this case?
>>(I do now!)
>>
>>Werner
>
>
>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 you know, thanks
>to alpha/beta, is that *all* are bad.  So which one would you try first?  In
>this position, at this depth, or at a deeper depth?  No way to know because
>*all* moves looked bad...

OK. You are right. But in this occasion, there is no chance at all to get a
good first move to try. So why not use the hash entry and spare on "if"?
Its a little bit faster and there is no harm and no use at all.

Werner



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