Author: Christophe Theron
Date: 17:03:55 07/30/04
Go up one level in this thread
On July 30, 2004 at 06:47:39, Gerd Isenberg wrote:
>On July 29, 2004 at 23:18:53, Walter Faxon 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.
>>>
>>>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
>>
>>
>>Will this detect when two like pieces have "traded places" in the repeated
>>position?
>
>Good point.
>
>I don't see how the "New Approach" handles "traded places" as well, because the
>list_of_moves doesn't contain piece information but only from/to squares.
>
>So occasionally the "New Appoach" may miss some repetitions, where rooks or
>knights have traded places. Whether this is practically relevant is another
>question.
>
>Gerd
It will also catch the cases where pieces have just traded squares.
Each piece is tracked individually by a vector summing up all of its moves. When
all vectors are 0, all pieces have been moved back to their "original" square.
The "master vector" is just a way to tell quickly if it is possible that there
is a repetition, and in this case all the individual vectors must be checked.
It is a "perfect" detector in the sense that it will not make any mistake.
Christophe
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