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Subject: Re: Easy moves

Author: Dieter Buerssner

Date: 12:58:46 04/20/01

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

>I'm trying to come up with a good algorithm for detecting "easy" moves.  The
>goal is of course to make obvious recaptures faster.

I am also in the process of thinking about this. Sorry, I cannot give an answer,
just a few comments.

>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.

Even if you don't use PVS, the same problem exists. With fail hard alpha-beta,
you will (almost?) allways only know, that the score of the remaining move is
not better, than the score of the PV move. With fail soft alpha-beta, you may
get better bounds, but in my experience, usually they will still be very close
to alpha.

>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".

I think this can't work. Especially with hash tables, that are not cleared
between moves, you will see very often, that the best move does not change in
the first 7 plies, even when it would have changed, when starting a search from
scratch without prefilled HTs.

Regards,
Dieter




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