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Subject: Re: Question about aspiration window

Author: Inmann Werner

Date: 09:53:12 08/14/98

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On August 14, 1998 at 10:33:05, Dan Homan wrote:

>On August 14, 1998 at 10:08:23, Inmann Werner wrote:
>
>>Question about aspiration window.
>>
>>I use Aspiration alpha-beta.
>>For the first searched move on a ply in deeper depth, I set alpha=oldbestvalue-x
>>and beta=oldbestvalue+x
>>Nothing unnormal.
>>
>>Now I found some positions, where my program lowers the evaluation of this first
>>move of a ply (till now the best!) always with x. (see above)
>>If I change x, it is the same until x gets really high, and i get a "true"
>>value.
>>
>>The disturbing thing on it is, that one ply deeper, the program should recognice
>>how bad this move really is, but it does not make a fail low! (If I get a fail
>>low, I research with open window)

-----

>I am going to guess here.  Your search cannot return a score less than
>alpha-x, so if you define a fail low as (score < alpha-x), you will never
>fail low (like you describe).  If you define a fail low as (score <= alpha-x),
>then everything should be ok.
>
> - Dan
>

Can i really not get a score less than alpha?

When I will use score<=alpha-x, this would only be good for the search on the
first move!? All other moves are searched with a close window. So, i think, i
always would get a fail low.
Am I right?

P.S: I looked at Minimax (some reference for me), and Minimax uses score<alpha-x
for a fail low detection. Is this a bug in Minimax?

Werner



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