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Subject: Re: repetition detection & hashing

Author: Robert Hyatt

Date: 20:38:54 01/15/02

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On January 15, 2002 at 21:50:52, martin fierz wrote:

>aloha,
>
>i have a question about repetitions, and it's only about the search itself, not
>about the game history: in my checkers program, to find repetition draws i keep
>track of the hash keys of the current variation, and if i find that the key for
>the current position has already ocurred before in the search, i return zero
>without searching further. i think this is the standard implementation?!
>anyway, i am wondering about the following problem: imagine you are searching a
>variation, and in the end you make a repetition. the program will stop searching
>there in the tree and assign the position a value of 0. now imagine that you
>have a different path of moves without a repetition which ends up at that node,
>probes the hashtable and returns 0. is this just my imagination, or can this
>happen and can it be bad?
>
>cheers
>  martin


It can happen.  As can the inverse, where you retrieve a real score from the
hash table but you can never reach the position because there is a three-fold
repetition between where you are and where you are going...




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