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Subject: Re: question about futility pruning and positional evaluation

Author: Ernst A. Heinz

Date: 13:09:32 12/07/00

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>If you use _any_ kind of pruning, you can perturb the root score.  Thanks
>to the transposition table that grafts parts of the tree into odd places.
>There is no way to anticipate which branches are useless _here_ but the
>hash results might improve the results over _there_.  And as a result, you
>can get different root move scores no matter how "sound" the pruning.

But the effects you describe, Bob, are rather due to the
hash-table usage than to the pruning. They might also
occur if you just change your move ordering.

Anyway, in the case of futility pruning at frontier nodes
with a remaining depth of 1 ply they hardly matter (if at
all) because it simply lifts inevitable "stand-pat" beta
cutoffs at horizon nodes up one level in the search.

=Ernst=



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