Author: Bruce Moreland
Date: 10:00:43 02/09/99
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On February 09, 1999 at 09:47:26, Dann Corbit wrote: >If, after location and execution of a 'best move' the computer's evaluation >function has a very large negative value (and possibly still dropping) can it >really be said to have *found* the correct move? > >It seems to me that we have two possibilities: >1. The program is on the right track, but has not really understood *why* the >move is good yet. In other words, "we have an accidental solution." >2. The move is actually not helping matters. You are going to lose anyway. >The test suite overlooked a good response by the opponent. > >In either case, I don't think a true best move was found. Shouldn't a best move >promise at least a draw and not a loss? Opinions? If there is more than one best move that leads to a desired game-theoretical result, there is nothing inherent in chess that would suggest a choice between them. The goal of chess is to maximize the game-theoretical outcome. If you can mate you should mate, otherwise you should draw. It doesn't matter how long it takes you, a mate in 45 is as good as a mate in 1. Most people would think that mating in a shorter time is important, but this is a layer of veneer that humans have added to the game. There is elegance in a short win, and there is practicality in it, since you want to score the point without offending your opponent, boring yourself, or risking losing it due to some external factor. In a chess program, returning "MATE - ply" as a score will guarantee the shortest mate the program can see, and this is an excellent heuristic if you are winning the game, but it is less good if you are losing, as anyone who has had a program throw all of its pieces away against you, before you even realized you had a win, understands. I think it makes sense to score some moves as better than others that lead to the same game-theoretical result, because you can talk about practical chances versus specific categories of opponent. The choice of move is necessarily subjective, but everyone can agree that a particular move would be most effective against the known classes of opponent. For instance, assuming no counterplay by your opponent, we can agree that it is almost always a good idea to win a queen and mop up quickly, and we'd score such a move as the best move in a test suite. But if you can also choose to win a pawn and go into a technically difficult but provably won ending, there is no difference, in a sense. We are really testing these programs against hypothetical opponents who have approximately known characteristics. bruce
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