Author: Slater Wold
Date: 09:54:08 02/05/04
Go up one level in this thread
On February 05, 2004 at 12:50:44, Robert Hyatt wrote: >On February 05, 2004 at 12:46:04, Slater Wold wrote: > >>On February 05, 2004 at 12:22:44, Bob Durrett wrote: >> >>>Referenced by: >>> >>>http://www.talkchess.com/forums/1/message.html?345569 >>> >>>> An alpha cutoff is what happens when you search the second move, >>>>> and you prove that if you play that move, your opponent has a move >>>>> he can play that will produce a score less than your "lower bound" >>>>> you established for the first move. There is no need to search >>>>> further. >>>>> >>>>> For example, after that +1 on the first move, you try the second >>>>> move and after trying the first move the opponent has in reply to >>>>> that move, you discover you _lose_ a pawn. The score is -1.0... >>>>> There is no need to search other opponent moves to produce a >>>>> score even lower than -1.00, because you already know this move >>>>> is at _least_ -1.00 and possibly worse, while the first move is >>>>> +1.00. You stop searching this move and move on to your third >>>>> choice... >> >>I haven't looked at many programs, other than TSCP, source, but I have a few >>question about this also... >> >>When do most engines call the qsearch? After selecting a move believed to be >>correct, of at the end of each search tree? > >When remaining depth = zero. IE if you want to do a normal 3 ply search, and >you have no search extensions, I make a move at the root, subtract 1 from depth, >and recursively call search. There I make a move for the opponent, subtract 1 >from depth and if it is > 0 (2-1 > 0 so true here) I again call search, >otherwise I call the q-search. At ply=3 I make a move for the program again, >subtract one from depth and now call the q-search since depth==0 after the last >subtraction. > >I did 3 full plies of looking at everything, but ply-4 and beyond are captures >only. > >> >>The reason I ask is, say you get a cutoff, because the 2nd move produced -1.0 >>(as in above), but after 4 checks and a capture, you regain that pawn & better >>position. > >Alpha/Beta is called a "depth-first" search strategy, because you _never_ stop >searching before you reach a tip position, therefore in the above you regain the >material before reaching the tip. So the tip, is where captures and checks stop? >>How do you prevent from not making a move that caused a cutoff, that actually >>leads to a better position? > >depth-first. See above.
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