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Subject: Re: Aspiration search

Author: Ulrich Tuerke

Date: 07:22:59 08/13/99

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On August 13, 1999 at 02:19:30, Scott Gasch wrote:

>Hey,
>
>I have a (stupid?) question about aspiration search.  I understand the concept
>is to atrificially limit the search window in an effort to prune faster.
>However, a value returned from Search(pos, a, b) will always be within the a-b
>window.  I.e. a <= value <= b.  How, then, does one tell if the value returned
>is bogus and needs to be re-Searched or whether it is good?  Which does a value
>== a or value == b mean?
>
>Thanks,
>Scott

Usually, the search window is defined without the boundary, i.e.
a < value < b   is an exact score; a = value or b = value means that you have
to proceed a verification search.

BTW, the alpha beta search of my program returns also values far outside the
alpha-beta region; these can be taken as bounds for the verification search.
I think that I remember vaguely that there are 2 kinds of alpha-beta
implementations: "fail soft" and "fail hard". I think that "fail soft" always
returns a value a <= value <= b ?
It seems that you are using "fail soft" whereas I use "fail hard".

I am sure that Bob Hyatt can help.

Regards, Uli



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