Eval scaling

Discussion of chess software programming and technical issues.

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Cardoso
Posts: 363
Joined: Thu Mar 16, 2006 7:39 pm
Location: Portugal
Full name: Alvaro Cardoso

Eval scaling

Post by Cardoso »

Hi everyone,

could someone please explain me the basics of evaluation scaling?
I suppose it depends on the number of pieces on the board.

Best regards,
Alvaro
Daniel Shawul
Posts: 4186
Joined: Tue Mar 14, 2006 11:34 am
Location: Ethiopia

Re: Eval scaling

Post by Daniel Shawul »

First you determine the game phase. (opening,midgame or endgame). This is usually done by looking at material (non-pawns). Then you scale up or down whatever makes sense in a particular phase. For instance, rump up king safety in middle game, and passed pawn score in endgame.
One popular way to achieve this is to keep two scores all the time, and then do an interpolation based on the 'phase' value. This forces you to scale every evaluation term. Or if you want, you can selectively scale up/down only some eval terms.