Author: KarinsDad
Date: 09:27:39 10/22/99
Go up one level in this thread
On October 22, 1999 at 11:57:01, Robert Hyatt wrote: [snip] >> >>If I had to guess, I would say that mobility is one out of several possible >>causal factors in a good position. However, it usually requires other factors >>such as material equality (or material advantage), square control, king threats, >>etc. In and of itself, a mobility advantage does not guarantee a good position. >>Just like in and of itself, a material advantage does not guarantee a good >>position. Each factor that leads to a good position is a subset of all of the >>factors and it is unlikely that any one factor takes precedence over all others. >>However, any given factor does not have to be present in order to have a good >>position (for example, you could be down a queen and about to checkmate or you >>might have only one move on the board and about to checkmate). >> >>However, a chess program searches the graph and keeps moves which lead to >>certain criteria and discards moves which do not. The fast searchers have a >>criteria of material gain (for the most part). If you could add a LOT of >>evaluation factors such as square control and mobility at an inexpensive cost >>similar to material gain, I think you will lead the game away from hidden >>pitfalls (beyond the event horizon) for you and towards hidden pitfalls for your >>opponent (on average, I doubt any algorithm could do this for all relatively >>equal positions) while at the same time, searching relatively deep. >> >>KarinsDad :) > > >My very first evaluation (for crafty) was material + mobility. It played _very_ >poorly. I added pawn structure. It _still_ played poorly. I came to the >conclusion that mobility was an effect of, and not a cause of, a good position. > >Some common eval 'terms' enhance mobility. Rooks on open files. Outposts. >Pieces not on the edge of the board. However, I have never been happy with >mobility as any sort of 'important' eval term. I use it for bishops as it >handles the 'good/bad' bishop case pretty nicely. But for other pieces, I don't >do mobility at all. For the queen it is _particularly_ bad. I'll take your word on it. It doesn't make much sense to me, but then again, there are a lot of things in this world that do not make sense to me, but that is the way they are. To me, it is a matter of possibilities. If I attempt to minimize the mobility of my opponent's pieces (i.e. prophylactic move) while trying to maintain or increase my own mobility, it would seem that I should be increasing my possibilities later in the game. However, the program has to have other factors as well. Code to prevent moves such as Rd1 xxx Re1 yyy Rd1 zzz Re1, etc. Evaluation terms for material gain; for not moving pawns in front of the king during the middlegame, but allowing them to move in the endgame; for square control (which helps in calculating safe mobility); in king safety; etc., etc., etc. Now by mobility, were you considering "safe mobility" (i.e. a square is only safe if your opponent cannot win your piece by moving it there, similar to a SEE) in your early versions of Crafty or "any mobility" (i.e. the piece can legally move there)? Also, in answer to your a4 move, the "do not move edge pawns in the opening" guideline code should counteract any gain in mobility. However, I have not written any "guidelines" on this type of code yet due to the difficulty in determining when such a guideline should be in effect vs. when it should not. My thinking is that I will add this type of guideline to my plan postprocessor as opposed to the eval function. KarinsDad :)
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.