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

Author: Vincent Diepeveen

Date: 17:06:38 12/04/99

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On December 04, 1999 at 01:35:52, Stephen A. Boak wrote:

>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.

I detect zugzwangs in my nullmove already, remember?

So those get detected already. We don't talk about a death&life
bonus for having the move here. It's just another bonus out of the
couple of the thousand that normally apply to an average middlegame position.

>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
>win).

Having the move in general is a big advantage as you can do
a move that gives you a position that is getting evaluated a lot better.

>   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.

This is of course true but making a move doesn't imply your opponent
can already make a move. Quiescencesearch will see after making a move
whether a too bad to be true.

I have a lot of eval taking care of this type of positions especially.
Positions where prospects are bad are statically evaluated a lot worse
already than the bonus of the move.

>   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?

It's an heuristic that's true in 99% of the positions that my program
searches obviously.

If a position is bad then usual programs nullmove. If a program nullmoves
then the other side has the move so gets the bonus.

So the sword cuts on 2 sides. Where you can nullmove normally to prevent
getting into a worse position, you now suddenly cannot as your opponent
gets the bonus instead of you.

>>
>>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).

Right. i'm just talking about this bonus. the other things i find objectively
crap. other bonuses listed below are basically to cover some heavy
weaknesses in evaluations of programs, or in case of evaluating moves
are causing unbalanced trees.

>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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