Author: Gareth McCaughan
Date: 15:13:33 06/06/00
Go up one level in this thread
On June 05, 2000 at 22:32:12, Albert Silver wrote: [I said:] >> I don't understand this argument. You could say the same thing about >> anything in the evaluation. Suppose the program has a choice between >> two moves; one leads to this position, the other leads to some other >> one-pawn-up position that *is* winnable. The other position evaluates, >> let's say, at +0.9. Then it matters whether this one evaluates at >> +0.4 or +1.0, no? >> > > Sure, but not here. There is nothing obvious about stating that a rook ending > with pawns on one wing and a one pawn advantage can't be won. There are > far too many exceptions in my opinion for this to work, so that this > knowledge is useless (as it is incomplete), and dangerous (as it may > lead to incorrect decisions). In order to validate this knowledge, I am > of the opinion that one would have to include far too many conditions > for it to justify the slowdown it would inevitably cause. It's not necessary to "validate this knowledge". Everything in the eval (more or less) is heuristic. Let's consider two chess programs. One of them has a rule that says something like "If the only pieces on the board are kings, rooks and pawns, one player has one pawn more than the other, and EITHER all of each player's pawns are connected on the K-side, OR all of each player's pawns are connected on the Q-side, and the player with one pawn more is deemed to be ahead by an amount x, then decrease the eval by x/2 or 0.5, whichever is smaller". The other doesn't. To save effort, I'm going to use the term "one-sided R+P position" to mean a R+P position that specifies the conditions in the rule. Now, there are three ways in which the programs could be of different strengths. 1. The "clever" program has a slightly slower evaluation function. It might be very slightly weaker as a result. 2. The "clever" program will evaluate some positions better, namely one-sided R+P positions which are unwinnable or much harder to win than they would be if they weren't one-sided. 3. The "clever" program will evaluate some positions worse, namely one-sided R+P positions which are winnable about as easily as they would be if they weren't one-sided. The "clever" program will be better if 2 outweighs 1 and 3. If, say, 75% of one-sided R+P positions are significantly more drawish than they would be if they weren't one-sided, and if the slow-down from having the rule is extremely small (both of which seem plausible to me, though I'm open to correction from better chess players or people who know more about writing computer chess programs), then the "clever" program will be better. I don't see how this is "useless" and "dangerous". Unless what you're saying is that actually most one-sided R+P positions aren't made any more drawish by being one-sided (and that no adjustment to the rule described above would change that), but that doesn't seem plausible to me. -- g
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