Author: Bruce Moreland
Date: 17:54:08 07/29/99
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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. 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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