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Subject: Re: Easy moves

Author: Robert Hyatt

Date: 19:41:22 04/20/01

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On April 20, 2001 at 15:34:01, Scott Gasch wrote:

>Hi all,
>
>I'm trying to come up with a good algorithm for detecting "easy" moves.  The
>goal is of course to make obvious recaptures faster.
>
>The obvious definition of an easy move is one where the score of the PV move at
>a certain depth is delta better than all the other moves at the root position.
>I use PVS, though, and because of the minimal window search on moves 2..N I
>don't come up with exact scores for some moves.


This is _not_ the way to do it. Find the Cray Blitz vs Belle game where
white has to play Bxh6 to force a draw rather than Qxb6 taking what appears
to be a free knight.  If you do what you suggest, Qxb6 will appear to be
easy and you will play it quickly.  And lose gloriously.

I go for "recapture of the piece just moved by the opponent to capture something
of mine."  If there is a fail-high or fail-low, I turn "easy" off to be even
more careful...

Look at the crafty source and grep for the "easy" string.  You will see where
it is set RootMoves() (root.c).  Note that if there are two or more ways to
recapture, this never even is considered easy...





>
>So I am looking for other definitions... right now I am experimenting with: if
>the first move searched never changed from plys 1-7 and it recaptures on the
>opponent's last move it is "easy".  This scares me a little, though... obviously
>this is not the sort of thing you want to get wrong.  Has anyone come up with a
>clever definition that doesn't involve extra searching?
>
>Thanks,
>Scott



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