Computer Chess Club Archives




Subject: Re: Parameter Tuning

Author: Don Beal

Date: 10:53:31 10/05/98

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On October 02, 1998 at 18:05:41, jonathan Baxter wrote:

>>BTW, we applied the same method to Shogi, and learnt piece values there.
>>That's directly useful, because Shogi doesn't have a standardised set of
>>values that programmers can pick up and use.
>I saw one of your papers on this (and liked it :).

Hey, we're going to get along real well :-) :-)

>One question I have is: the piece values drift
>an awful lot, with the drift seeming to reduce only with the decrease in step
>size. I was wondering, if you keep the step size constant (but small) and run
>for 100's of 1000's of games, do the pieces swap their relative ordering a lot
>or do they finally settle to a constant relative ordering?

With fixed learning rates (aka step size) we found piece values settle to
consistent relative ordering in around 500 self-play games.  The ordering
remains in place despite considerable erratic movements.
But piece-square values can take a lot longer - more like 5000.

The learning rate is critical - it has to be as large as one dares
for fast learning, but low for stable values.  We've been experimenting
with methods for automatically adjusting the learning rate. (Higher
rates if the adjustments go in the same direction, lower if they keep
changing direction.)

The other problem is learning weights for terms which only occur rarely.
Then the learning process doesn't see enough examples to settle on
good weights in a reasonable time.  I suspect this is the main limitation
of the method, but it may be possible to devise ways to generate
extra games which exercise the rare conditions.

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