Author: Robert Hyatt
Date: 20:07:51 07/29/99
Go up one level in this thread
On July 29, 1999 at 21:47:26, Peter McKenzie wrote: >On July 29, 1999 at 20:54:08, Bruce Moreland wrote: > >> >>On July 29, 1999 at 18:58:12, Ian Osgood wrote: >> >>>Do other program authors curtail the search when there is a forced move at the >>>root? >>> >>>How do you detect that a root move may be forced? >>> >>>Could you compare the values of the best and second-best root moves after a >>>search iteration to detect a forced root move? (Granted, the second-best score >>>won't be accurate due to alpha-beta, but I figure that if the difference was >>>greater than a queen's value, you could still conclude that the best move was >>>forced.) >> >>The only sure way to do this is if there is only one legal move. > >Another safe one is if you figure out that all other moves get mated instantly. >I don't do that yet in LambChop, but it doesn't sound too hard. How would you discover this? You get a score for the first move (the one you think is obvious) and all the rest fail low and return alpha. > >If all other moves return a mate score, its probably a pretty good heuristic to >play the move that doesn't. This could lead to allowing a quicker mate >sometimes (due to extensions etc) but I think I'd be comfortable with that risk >:-) > >> >>Any other technique is going to leave you open to cases where you can make >>mistakes, and I'm sure there are cases where you'll miss a win or make a losing >>move, and you won't do this if you'll think longer. >> >>If you decide that you can live with walking into losses and missing wins, the >>first question is why did you decide that you can live with this. >> >>One reason is to impress the humans, or avoid having them call you stupid. This >>is a valid reason, in my opinion. >> >>Another reason is that you save time on the clock this way, and in a computer vs >>computer game with both sides thinking on the opponent's time, you could >>initiate a sequence of instant moves this way, rather than walk into a situation >>where your opponent has a sequence of instance moves. I don't know if the >>strength gain is higher from catching mistakes, or having extra time or going >>for an instant-move sequence, but I'll bet on the latter. >> >>Now the question is deciding what is forced. An obvious clue is that the search >>sticks with one move more or less forever. Another clue might be that all of >>the other moves can be refuted in a small amount of time, but I haven't >>experimented with this. And if you need to restrict this because you are doing >>forced moves that aren't really forced, you can restrict it so that you only do >>this if the program wants to make a recapturing move. >> >>bruce
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