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Subject: Re: Question about aspiration window

Author: Dan Homan

Date: 11:18:13 08/14/98

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On August 14, 1998 at 12:53:12, Inmann Werner wrote:

>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

Sorry,  I meant use (score <= oldbestscore - x) as your fail low condition.

 - Dan

>always would get a fail low.
>Am I right?
>
>P.S: I looked at Minimax (some reference for me), and Minimax uses scorefor a fail low detection. Is this a bug in Minimax?
>
>Werner



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