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Subject: Re: Unexpected problem with futility pruning ?

Author: Tord Romstad

Date: 15:12:01 12/29/03

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On December 29, 2003 at 16:49:35, Vincent Diepeveen wrote:

>On December 29, 2003 at 15:26:27, Geoff wrote:
>
>>Hi
>
>Just kick it out and you have no problems anymore.
>
>I'm not using it in DIEP. DIEP is not using lazy eval either.

I tend to agree.  I used futility pruning in the past, but found it too risky
positionally
as well as tactically.  You simply don't know a lot about a move before you
execute
it on the board, and it is rather dangerous to prune it without more knowledge.

I've found it much more effective to first make the move, evaluate the resulting
position, and only then decide whether the move deserves to be pruned.  By
comparing
the eval (or better yet, the different components of the eval) before and after
the
move was made, you have a much better basis for making pruning decisions.  This
is of course more expensive than futility pruning, but in my experience it is
worth
the cost.

Futility pruning combined with lazy eval seems even more dangerous to me.  When
pruning a move without examining it closely, you should definitely know more
about
the position than the value of the lazy eval.

Tord




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