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Subject: learning evaluation weights (was Re: Genetic algorithms for chess?)

Author: Don Beal

Date: 12:33:00 05/22/98

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On May 19, 1998 at 12:45:59, Komputer Korner wrote:

>There was an article on refining piece values in the ICCA journal last
>year, but there was a major flaw in the research becuase they used
>lookahead search of only 4 plies and that is not enough for knight
>manoeuvers.

The article was "Learning Piece Values Using Temporal Differences"
ICCA Journal, Vol 20, No 3, Sept 1997.

I was concerned to find the inaccurate comment "major flaw in
the research".

Whilst I don't think "inkompetent computers :-)" are likely to
damage reputations too seriously, I'd just like to respond...

The intention of the paper was to present the learning *method*,
and its ability to start from no information whatsoever about piece
values and obtain effective ones.  The values learnt were *not*
the result of the research; the fact that the method obtained
sensible values as opposed to ineffective values *was*.

That said, however, the values were, of course, of interest, which
is why we reported them.

We made no claim that the values would be the optimum values
for larger search depths, nor, as we commented in the paper,
optimum if the evaluation included positional terms.  (Our
"proof of principle" experiment used piece values as the only
evaluation!)

As regards the lookahead depth, we didn't try large depths, but
over the range of depths we did try, we found that the depth of
search had only a small effect on the values obtained.  This is
perhaps less surprising when one realises that the learning method
reacts to *positions* and the associated game outcome, not to move
sequences that might, or might not, occur between the position and
the end of the game.


Other people are experimenting with TD learning - if any are
reading CCC, perhaps they have values for comparison?

Don Beal.



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