Author: Robert Hyatt
Date: 05:52:04 07/30/99
Go up one level in this thread
On July 30, 1999 at 00:28:06, Ed Schröder 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. > >Search the first iteration without alpha/beta. > >Ed Schroder > How does that help? Peter said a move is forced if all other moves lead to mate. Note to mate-in-one, but to mate-in-any. 1 ply search won't find this. > > >> >>> >>>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
This page took 0.02 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.