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Subject: Re: Programmers: please check my alpha-beta algorithm

Author: Patrick N

Date: 09:44:12 09/29/03

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On September 29, 2003 at 12:35:01, Gian-Carlo Pascutto wrote:

>On September 29, 2003 at 12:32:53, Patrick N wrote:
>
>>On September 29, 2003 at 11:54:55, Gian-Carlo Pascutto wrote:
>>
>>>On September 29, 2003 at 11:49:20, Edward Seid wrote:
>>>
>>>>         score = -AlphaBeta(deep - 1, -beta, -alpha)
>>>
>>>[...]
>>>
>>>>         ' The following lines are what I need feedback on... are they correct?
>>>>         If alpha >= beta Then
>>>>            Return alpha
>>>>         End If
>>>>         If score > alpha Then
>>>>            alpha = score
>>>>         End If
>>>
>>>Reverse them.
>>>
>>>E.g.
>>>
>>>if score > alpha then alpha = score;
>>>if alpha > beta then return alpha;
>>>
>>>--
>>>GCP
>>
>>I agree with reversing them, but you also want the second line to read:
>>if alpha > beta then return beta;
>>
>>This way if the score exceeds beta (fail high) you return beta
>>-Patrick
>
>No.
>
>There is no need whatsoever to return beta there.
>
>--
>GCP
You are right.  Depends on if you are doing fail-hard or or fail-soft.  If you
return beta, you are doing fail-hard.  With alpha, fail-soft.  I find fail-hard
to be easier to understand.  I like to know that my search is going to return a
value that is somewhere between alpha and beta.  :)
-Patrick



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