Author: Miguel A. Ballicora
Date: 11:28:00 12/18/01
Go up one level in this thread
On December 18, 2001 at 13:09:21, Miguel A. Ballicora wrote:
[snip]
from the EPD standard:
>A value of -32767 indicates an illegal position. A stalemate position has a
>centipawn evaluation of zero as does a position drawn due to insufficient
>mating material. Any other position known to be a certain forced draw also has
>a centipawn evaluation of zero.
Now, the EPD standard is seriously broken. I just thought for a little while
after I post. What kind of evaluation is expecting me to return when
my program receives this position to be analyzed?
[D]k6R/8/K7/8/8/8/8/8 b - -
On the other hand, I did a search on CCC and I found a piece of an article,
supposedly written by Steven Edwards (author of the EPD standard} on how to
convert the evaluation from the the EGTBs to EPD evaluation. To my surprise,
unless the EPD standard changed along the way, what it is said contradicts the
current EPD standard. What is going on?
This is part of the article you can find at
http://www.it.ro/ccc_search/ccc.php?art_id=25216
My comments are between {}
Regards,
Miguel
-----------------------------------------------------------------------------
EPD Value transformation:
For those incorporating these tables into a chessplaying program, it is
suggested that the appropriate value transformation be used to convert
from
the single byte encoding scheme to the signed sixteen bit integer EPD
(Extended Position Description) standard. Programs that use EPD help
support
quick integeration. Fortunately, conversion to EPD evaluations is easy
to do.
Description Signed Byte EPD Signed Word
----------- ----------- ---------------
unknown -128
transition -127
lost-in-0 -126 -32767 (checkmated) {This value is illegal position!!}
lost-in-1 -125 -32765
lost-in-2 -124 -32763
...
lost-in-N (N - 126) ((N * 2) - 32767)
...
lost-in-125 -1 -32517
draw 0 0
mate-in-126 1 32516
...
mate-in-N (127 - N) (32767 - (N * 2) + 1)
...
mate-in-3 125 32762
mate-in-2 125 32764
mate-in-1 126 32766
illegal 127 -32768 {This value is out of range of the current EPD stadard!!}
The EPD signed 16 bit words are usually interpreted as centipawn values.
However, scores less than -31744 are treated as forced losses while
scores
greater than 31743 are treated as forced wins.
More information about the EPD standard can be found in the appropriate
section of the Portable Game Notation standard (pub/chess/PGN/Standard
at the
ics.onenet.net ftp site).
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.