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Subject: Re: Unable to improve alpha

Author: Scott Gasch

Date: 11:24:15 07/25/04

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On July 25, 2004 at 09:10:19, Stuart Cracraft wrote:

>So at the root, in the opening position, I play e4.
>At the third ply of iterative deepening, the program
>hits the position after 1 e4, e5; 2 Qh5, Bc5; 3 Qxe5. No
>null move has been played here due to being in check.
>The program now cycles through the only legal black
>replies of 3 ... Ne7, 3 ... Be7, 3 ... Kf8, and 3 ... Qe7.
>Going into this, alpha is -6 from the previous position.
>None of these moves improves alpha and this value is
>returned with no best move stored in the hash table.
>
>My question is: is this a problem or expected given
>the position?
>

This is a fail low node and they are quite common.  In your tree you should now
see the the move leading to this position (Qxe5) fail high (return a score >=
beta).  If you have good move ordering you searched that move first.  Now you
can cut off here and not search the rest of white's moves on that ply.

Scott



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