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Subject: Re: Compact encoding of chess positions

Author: Reinhard Scharnagl

Date: 23:11:33 03/04/05

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On March 04, 2005 at 14:45:46, Chris Welty wrote:

>Your idea of restricting the allowed sets of pieces on the board is brilliant,
>because most of the legal positions in chess have really silly combinations of
>pieces.
>
>Generally you need to use the maximum length of the encoding rather than the
>average length. If you know enough about the encoding to calculate the average
>length you know enough to calculate the exact number of positions and can encode
>the positions by giving each position a number.
>
>I tried it with a slightly different restriction: Each side may have no more
>than 7 officers (officer=Q/R/B/N). An upper bound on the number of positions
>with this restriction is 2.3754e+043 and it can therefore be encoded in 144.091
>bits. Probably this can be reduced by another 1-2 bits by someone really
>determined.
>
>Is a 7-officer maximum realistic in actual games?

Hi Chris,

a) if one player is superior to the other in practical games there could be
easyly raised more the seven officers in the piece set of the better player.

So I think that such a restriction would be somehow unrealistic.

b) Of course you can conclude from a maximum count of positions to an existing
encoding length when providing such a huge look up table for all existing chess
positions. But what I experimented with has been a realistic encoding scheme
without such an utopic look up table.

Reinhard.



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