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Subject: Re: Question about aspiration window

Author: Dan Homan

Date: 07:33:05 08/14/98

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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

>
>I removed hashing and null-move, but it is the same.
>If i search the first move of a ply with a full window, everything gets ok, but
>slow!
>
>I am sure, it is a failure in my thinking of aspiration alpha beta.
>Has anybody an idea, what could be wrong, where I could search the failure?
>
>Werner



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