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Subject: Re: repetition detection & hashing

Author: martin fierz

Date: 21:08:19 01/15/02

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On January 15, 2002 at 23:38:54, Robert Hyatt wrote:

>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...

so... is there a solution to this problem? or is it just tacitly assumed that it
"never happens"?

cheers
  martin




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