# Computer Chess Club Archives

## Messages

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

Author: Vincent Diepeveen

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

Go up one level in this thread

```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?

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?

>not automatically make the position a good one.  It simply minimizes the

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).

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

```