Author: Robert Hyatt
Date: 20:42:23 07/30/99
Go up one level in this thread
On July 30, 1999 at 09:39:11, blass uri wrote: > >On July 30, 1999 at 08:52:04, Robert Hyatt wrote: > >>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. > >1 ply search will find part of the forced moves and it is better than nothing. > >You cannot find all the forced moves because always there are cases when the >mate is too deep for your ptogram. > >Uri I wouldn't disagree with that... but 'better than nothing' is _not_ good enough when trying to choose forced moved. IE the primary purpose of this idea is to make 'obvious' moves quickly to save time. If you use such a simple test for mate, you will only discover forced moves near the end of the game. And at that point in the game, saving time is not important... I have a "move instantly if there is one legal move" rule in crafty. I doubt it gets exercised once in every 10 games. This sort of 'forcing' test is not going to be very effective, because the idea becomes "a move is forced if all but one move is found to lead to mate by a trivial search." Many mates are not found by 'trivial searches' and such positions won't appear to be forced. Of course, it is all moot anyway, IMHO. Such move ordering was used 20 years ago and not found to be particularly great, when compared to other better approaches...
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