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Subject: Re: Automated Tuning

Author: Don Dailey

Date: 15:27:06 01/12/98

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On January 12, 1998 at 17:43:30, Stuart Cracraft wrote:

>What are the experiences of this group with automated tuning?
>I'm thinking of two specifically:
>   - temporal difference learning (Tesauro-style) or best-fit
>     (Nowatzyk/Deep-Blue style) based on master games
>   - survival-of-fitest round-robin matches between same program
>     with slightly different coefficients or weights for evaluation
>     function

Hi Stuart,

I played around with genetic algorithms for this.  It was a heck of
a lot of fun but nothing came out of it.  I think the problem has
to do with the incredible slowness of the fitness function where
you have to play games to measure fitness.   1 or 2 games is a
very poor fitness function.

But nevertheless, I did come up with interesting results.  The
process eventually returned realistic values for the pieces which
gave me some confidence that at least in principle the idea might
be workable.

John Stanback also played around with this stuff.

I did something similar with master game databases with Larry Kaufman.
We looked at hundreds of material signatures and computed values for
all the pieces using the genetic algorithm.  Our results were based
on which piece combinations tended to win a lose.  I remember little
except that the numbers were very normal looking, even more so than
the prior experiment.   The one odd thing was that the bishop pair
got a very high value.  But our program over the years has kept
the value of the bishop pair, I don't think the number was very far
off now.  It came to almost half a pawn.  We believe the right value
is close to this.  But of course there are numerous factors involved.
I remember a master once telling me that 2 bishops were more than a
pawn better than 2 knights so this value may not be ridiculous.  We
also believe the bishop and knight (not considering the bishop pair)
is about the same with perhaps a very slight nod to the bishop.  Also
there are conditions as we all know where a knight is much better and
so on but I'm talking about the "average" case with nothing else known.

We have developed a sort of theory of piece cooperation you may be
interested in hearing.  The main point is that similar pieces do not
help as much, in other words 1 knight is good, 2 knights are not quite
twice as good.  But 2 bishops are completely different pieces
because they are on different color squares.  The second black squared
bishop for instance would be worth very little compared to the first.

Queens share some powers with bishops and rooks so queens might be
better with knights.

Our program gives a rook pair penalty, a knight pair penalty, a
bishop pair bonus and others.   Most of these numbers are quite
small and probably affect things very rarely.  Most people are
surprised at the rook pair penalty but I've had a couple Grandmasters
after scratching their heads a bit say it made a lot of sense.

One important note:  No matter what numbers you use they must make
a lot of sense in relation to other things.  If you have very
conservative evaluation you would be foolish to use 1/2 pawn for
bishop pair bonus because your program would be "heel bent" to
hang on to the bishop pair and seriously compromise it's position
to do this.

- Don

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