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Subject: Assymetry & Bonus in Static Eval? (after a Sac or whenever)

Author: Stephen A. Boak

Date: 22:35:52 12/03/99

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I do not understand about assymmetric evaluations or giving a bonus for the side
to move.  Please provide a brief explanation, thanks!

>On December 03, 1999 at 21:31:09, Vincent Diepeveen wrote:
>Except for an experiment giving the side to move a bonus to some extend
>i've never been assymmetric. When I threw out this bonus too, then
>diep improved a lot in level.
>Logical one would say a bonus for having the side to move is good,
>but it never worked for DIEP.

Why is it logical to give a bonus for having the side to move?

1) If a position is zugzwang, then the side to move will lose regardless of
having the right to move.

2) Having the right to move gives the side to move a choice of direction.
Having a choice of move allows the side the move to select its own destiny
(meaning path) but not necessarily its own ultimate destiny (meaning draw or

   For example, if the position is bad for the side to move, how does having the
move in a bad position make it more likely that the position will improve
(meaning get better that it is at the moment) because of the move choice by the
side to move?

   In a bad position, selecting the 'least bad' move among many bad moves does
not automatically make the position a good one.  It simply minimizes the
negative aspects of the bad position after the move is made.

   Giving a bonus for the side to move might be overly optimistic for the side
with the bad position and the right to move.

Do I understand correctly--for each static evaluation of a single position (leaf
node, I guess), the program evaluates based on material and positional factors
without regard to which side is on the move?  Then, some programmers like to add
a bonus for the side to move?

>Never figured out why. Did i have a bug?
>Apart from this discussion, from which i don't know whether it's good to have,
>being assymetric becasue white might be a human and black a computer,
>i am against using an assymmetric evaluation function for that.

Seems to me there are various types of assymetry in evaluation that a programmer
might try to incorporate (are these the kinds of assymetry you are discussing?):

1) The side to move gets a bonus (or penalty).

2) The side to move, if in the better position, scores moves in a manner that
gives more contempt for a draw (goal is more to win, and less to draw--i.e.,
more contempt for a drawing move/line).  The side to move, if in the worse
position, scores moves in a manner that gives less contempt for a draw (goal is
more to seek a draw, and less to try to take risks to win).

3) Moves may be scored differently, depending on the perceived nature/strength
of a known opponent.   Examples of differences in known opponents:  human vs.
computer; human, maybe a GM, with certain propensity for playing some types of
positions well, and some not so well; computer with certain propensity for
playing some types of positions well--perhaps open; and some not so
well--perhaps closed or gambits requiring long term contempt for material in the
all-out seeking of a victory).

Any enlightenment on the above subjects would be much appreciated.  Then I can
follow the discussions with improved understanding and even more interest.
Thank you.

--Steve Boak

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