Author: Robert Hyatt
Date: 17:21:44 01/13/04
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On January 13, 2004 at 17:27:46, Alessandro Damiani wrote: >>You need to be _very_ careful doing what you describe. It leads to a >>scoring discontinuity, or a "boundary condition" that can be very bad >>with minimax/alpha-beta search. If you know what a discontinuous function >>is, you just defined one (IE in Laplace transforms, you see "unit step >>functions" that have this property.) The problem here is that when you >>are searching positions where you _cross_ the boundary in the search, the >>program gets to pick when and where it crosses, and since you are talking >>about a positional score of +/- 3 pawns or more, what it might do is give >>up two pawns rather than lose the 3 pawn advantage. Not a good plan, >>usually. Your evaluation function _really_ should be a continuous function >>that has no such "discontinuities". >> >>IE you might do just fine where you have lots of pieces and use that >>trick, and once there are no pieces, you are also OK. But around the >>"edge" where you go from "have to have not" the search can do some amazing >>things to use that discontinuity to produce results wildly different from >>what you would normally expect to see. IE early in Crafty I did that for >>endgames, where material <= N. And at the transition point, I saw some >>_ugly_ ideas pop out of the search. Now it is a smooth transition from one >>phase to the next with no sudden large jumps.. >> >>I think Hans Berliner wrote a paper about this topic but I can't recall the >>title for the life of me... > >SNAC (Smoothness, Non-Linearity, and Application Coefficients). I remember the >content, but I don't remember where I put it. Maybe in one of the boxes that are >in the cellar since I relocated. ;-) > >Alessandro Good man, good memory. :)
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