Author: Robert Hyatt
Date: 08:55:23 04/28/03
Go up one level in this thread
On April 27, 2003 at 18:06:35, Tim Foden wrote: >On April 27, 2003 at 10:56:45, Robert Hyatt wrote: > >>On April 26, 2003 at 19:15:04, Drexel,Michael wrote: >> >>>Today I started an interesting experiment. >>>A match Chessmaster 9000 against Shredder 7.04 in Chessbase GUI with >>>over-optimistically settings for The King 3.23. >>>With this settings The King engine evaluates his positions almost always as >>>better for himself, except it is completely lost. >> >>You are overlooking a key point. The alpha/beta algorithm is relative to >>the initial score. If a program starts off at +3.0, and another program >>starts off at 0.0 in the same position, the two programs can play >>identically. All alpha/beta tries to do is maximize the raw score at the >>root, whether it is +3 or -3 is irrelevant... > >This is of course true. And the effects on a particular engine would depend >much on the way that the piece scores are used. > >However, he isn't just adding +3.0 to the score of one side... he is (in effect) >adding <some-const>*pieces. So every time otherwise equal material is swapped, >the engine will believe it has lost relative to the opponent. I thus this would >make the engine less likely to exchange material, and this must modify the way >it plays... it would try to make more positional compensation before swapping, >for example. > >Also, if it used the piece-material values in some way for king safety, then it >may make the king safety into a kind of a-symmetrical one. > >So, basically, I don't agree that it will have no effect at all. :) It depends on how it is done. For example, in crafty I have the usual "trade pieces if ahead in material, trade pawns if behind in material." That inflates the score (or deflates the score) in endings because if it is a piece ahead, it will have an even bigger + score as pieces are removed. And these scores are generally _correct_ in that a bigger score is better, but the absolute value of the score is not particularly significant, since I have never seen anyone say "if you are ahead a piece and you have traded all pieces away except for your extra piece, give yourself another pawn advantage." Yet all programs do this. So, again, ignore the _value_ and just take the best move as the "best move according to the program." If you believe the "white is +.5 pawns better" then you are in a grey area, at best... If you believe just "white is better" you might be safer, but even then it is not so clear. > >Cheers, Tim.
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