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Subject: Re: Backward Pruning

Author: Robert Hyatt

Date: 07:34:23 10/23/99

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On October 23, 1999 at 09:57:41, KarinsDad wrote:

>On October 23, 1999 at 05:30:05, Alessandro Damiani wrote:
>
>[snip]
>>
>>Forward pruning is the opposite of backward pruning. With this in mind I would
>>say null-move is forward pruning: it prunes before the subtree is searched.
>>
>>Forward pruning should be the name of a general technique and not only for
>>excluding moves from search (like Qsearch).
>>
>>I would make two classes: forward pruning, backward pruning.
>>
>>Alessandro
>
>In the tens of thousands of posts I have read here, I do not think I have ever
>read the term backward pruning (yet another reason to have a separate technical
>section).
>
>Could you please explain what backward pruning is?
>
>Thanks,
>
>KarinsDad :)


Backward pruning is what alpha/beta does to minimax trees.  As you 'back up
scores', you can make decisions about which moves absolutely don't need to
be searched, because of alpha/beta bounds and the score just backed up for a
move.  This was the term originally used in the first paper on alpha/beta and
it has been used ever since to apply to programs that do searches and then use
the results of those searches to eliminate other branches without searching
them.



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