Author: Peter McKenzie
Date: 18:47:26 07/29/99
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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. 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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