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Subject: Re: Interesting mate test for hashing

Author: William Bryant

Date: 08:40:57 09/11/99

Go up one level in this thread


On September 11, 1999 at 11:26:45, William Bryant wrote:

>On September 11, 1999 at 00:19:40, Robert Hyatt wrote:
>
>>That seems to be backward.  If score > beta, the _current move_ you just
>>searched failed high.  That move should be stored in the hash table to try it
>>first the next time you search this position.  The problem we are discussing
>>is the _other_ case.. the one where you search all movs and still end up
>>with best == alpha, which means all moves were bad...
>
>Alright,
>  on re-rereading, let me try this again.
>
>You completed a ply and found no new alpha (failed-low).
>alpha is already greater than a constant MateScore (Mate - some constant).
>
>You store this in the hash table as follows.
>
>if (alpha>MateScore)
>	store the value as MateScore and the flag as hash_Lower to show that this
>	is the lowest value this position could have.
>	Because you failed low, there is not best move.
>
>if (alpha<-MateScore)
>	storethis normally, with the flag hash_Upper to show that this is the
>	highest value this position could have.
>	Again, because you failed low, there is no best move.
>
>Closer?
>

Actually, One more try-- it is the extremes on a fail low node that cause
	problems when abs(alpha) > MateScore

so,
if (alpha>MateScore)
	store the value as MateScore and the flag as hash_Lower to show that this
		is the lowest value this position could have.
	Because you failed low, there is no best move.

if (alpha<-MateScore)
	store this with a score of -MateScore,
		with the flag hash_Upper to show that this is the
		highest value this position could have.
	Again, because you failed low, there is no best move.

Even Closer?


William
wbryant@ix.netcom.com




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