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Subject: Re: How to extend if only one reply?

Author: Scott Gasch

Date: 13:28:41 01/23/01

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On January 23, 2001 at 14:59:40, Severi Salminen wrote:
>
>I want my engine to also solve these mate in 3871 positions fast :) So: how do
>you guys extend if there is only one legal reply in node. Obviously you have to
>check the legality before trying that move. So do you allways when the king is
>in check check the legality of all moves and if that results one legal move you
>extend? Are there another ways to do this?
>

I do this by calling a special move generator when side to move is in check.
This generator considers king escapes, moves that can block the check and moves
that can capture the checking piece.  It also returns the number of checking
pieces so I can do the amy-style "double-check" extension.

If the evasions generator returns only one move, I extend.

Don't extend too much on this -- the odds are the side putting you in check just
got an extend last ply.  Now you extend again for one reply... and he checks
again... and you have very deep, stupid lines of pointless checks.  I scale this
extension back to partial ply after iteration depth.

Scott





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