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Subject: Re: A New Approach to Draw Detection by Move Repetition in Computer Ches

Author: Ricardo Gibert

Date: 16:25:37 07/29/04

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On July 29, 2004 at 19:22:44, Ricardo Gibert wrote:

>On July 29, 2004 at 17:34:11, Christophe Theron wrote:
>
>>On July 29, 2004 at 14:07:10, Robert Hyatt wrote:
>>
>>>On July 29, 2004 at 06:26:52, Gian-Carlo Pascutto wrote:
>>>
>>>>http://arxiv.org/ftp/cs/papers/0406/0406038.pdf
>>>>
>>>>I stumbled onto this when doing a search for Axon.
>>>>Not seen it mentioned here yet.
>>>>
>>>>They also have a paper about hashing out which I can't
>>>>download.
>>>>
>>>>--
>>>>GCP
>>>
>>>
>>>Doesn't strike me as particularly interesting.  IE it almost seems that they
>>>don't realize that most programs store positions in a repetition list as 64 bit
>>>Zobrist integers...
>>
>>
>>
>>Actually I think it might be interesting.
>>
>>Recently, when I was rewriting the core of the Chess Tiger engine, I realized
>>that I could get even more speed by not computing the hash keys during the
>>quiescence search for example.
>>
>>In my case, it would have meant some more changes in the engine and the way I do
>>QSearch. But for some programs, it could be interesting.
>>
>>The problem then is how do you check for repetitions?
>>
>>If you allow checks and escape from checks in your QSearch, and if you actually
>>extend them in some way, you have to detect repetitions.
>>
>>So a lightweight, hash key free, repetitions detector is a must in this case.
>>
>>It could also be interesting for people who want to write a very small chess
>>program for portable units.
>>
>>But I think there is a better method than the one given in the paper. I would
>>use an array of integers, one per piece on the board. The array starts filled
>>with 0. Every time a piece is moved I would add the move vector to the integer
>>in the array.
>>
>>A repetition is detected when all the array is filled with 0 (nul vectors). It
>>is possible to use a "master vector" that receives all the individual vectors
>>after every move. One has to check the whole array only when the master vector
>>is nul, otherwise there cannot be a repetition.
>
>Maybe I've misunderstood, but this seems to me to be a method of testing whether
>the current position is a repetition of one particular previous position rather
>than whether the current position is a repetition of any one of the entire set
>of previous positions. I don't see how it can be made to work.

Actually, I do now see how it can be made to work, but it would be far too
inefficient.

>
>>
>>This method also works backwards (from the current move back to the last
>>irreversible move), but avoids any search in the concatenation list.
>>
>>It should be significantly faster than their method.
>>
>>Now I should write a paper. :)
>>
>>
>>
>>    Christophe



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