Author: Christophe Theron
Date: 17:00:04 07/30/04
Go up one level in this thread
On July 29, 2004 at 19:25:37, Ricardo Gibert wrote:
>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.
You start from the current position (what I call the current position is any
position you reach at the end of your search) and work your way backwards until
you either find an irreversible move or detect a repetition.
It is more efficient than the way described in the paper, and in the case where
you do not compute a hash key in the QSearch it could be a very efficient method
of detecting draws by repetition. Maybe there is a better one, I don't know.
Christophe
>
>>
>>>
>>>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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