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Subject: Re: question about futility pruning and positional evaluation

Author: Robert Hyatt

Date: 06:45:45 12/09/00

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On December 09, 2000 at 05:56:25, Georg v. Zimmermann wrote:

>>>
>>>But this wont happen if your margin is large enough. As large as your largest
>>>position scores. As explained by Ernst. Very simple. And accurate.
>>
>>
>>Yes... but if the margin is "big enough" then you don't have futility pruning,
>>either.  That is the problem.  And if you eliminate _one_ node from the tree
>>search, you stand the chance of perturbing the score that eventually backs up
>>to the root of the tree, due to the hash table.
>>
>>The problem with "big enough" is that for some programs, "big enough" might be
>>a pawn or two.  For other programs it might be way more than a queen.  Such a
>>window effectively disables futility pruning.  For those that want to produce
>>very large positional scores.
>
>What I am doing is to set value = fmax = eval(); instead of materialeval(). That
>way your margin can be the maximum eval change in 1ply only. This obviously only
>works if your eval() is very fast. If not, you can try to write another
>fasteval() function which only uses those eval parts than can get very big, king
>safety for example. I got good results with that.
>
>Regards,
>Georg v. Zimmermann


The problem is that an eval can change a _lot_ in one ply, for some programs.
IE mine could change by at least a queen for the right kind of capture.  Or
the right kind of pawn move.



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