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Subject: Incomplete egtbs can be harmful

Author: Leen Ammeraal

Date: 04:18:29 11/06/01


In the directory containing my Nalimov databases,
when I give the command

  dir kqr*.*

I obtain the following output:

KQRKNBB  EMD       296,182  10-04-99  2:31p KQRKNBB.EMD
KQRKNBW  EMD       211,121  10-04-99  2:31p KQRKNBW.EMD
KQRKQNBW EMD    21,727,039  04-11-99 11:37a KQRKQNBW.EMD
KQRKQNBB EMD    37,812,136  04-11-99 11:40a KQRKQNBB.EMD

This suggests that I have no file for the KQRkr endgame,
which may very well be the case, since I know that
my set of 5-man files is incomplete.

I had always thought that this should not be a serious problem,
because my program will probably deal well with KQRkr
endgames without any egtb. However, I just found that there
are a serious problems in the case of promotion moves,
as in the following trivial position:

[D]8/8/8/8/6r1/8/3K1kp1/R7 b - - 0 3

My program sees that black deserves a very high score,
derived from the egtb, but fails to make the trivial
move 1. ... g1Q because it does not find an entry
for the resulting position in the egtb, and because
the computed score after this promotion move
is lower than the egtb score retrieved after the
move Rg3, so the latter move is made and the
game results in a draw instead of in a win for
black. Has anyone encountered similar problems?
It seems to me that for any egtb file with
pawns, there should be a corresponding file
for the case that one of the pawns has turned
into a queen. If not, the result may be
completely wrong, as in the above example.
Leen





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