Author: Robert Hyatt
Date: 05:50:42 07/30/99
Go up one level in this thread
On July 30, 1999 at 06:16:34, blass uri wrote: > >On July 29, 1999 at 23:07:51, Robert Hyatt wrote: > >>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. > >You can get a score for the 2 best moves and not only for the first move. >If you use the 2 options usually only for 1/10000 of your time then in most of >the cases you are 0.01% slower but when the evaluation of the second best move >is mate against yourself you can be faster. > >Uri No you can't. Alpha / beta doesn't do this. If you study programs, the first move at the root takes well over 50% of the total search time. To get the score for the second-best move will take this much time _again_ above and beyond what would normally be taken. IE in a normal search, with 30 moves at the root, 3 minutes per move as the target time, move1: 90 seconds move2-30: 90 seconds to get the score for the second-best move: move1: 90 seconds move2: 90 seconds move3-30 87 seconds A _huge_ loss.
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