Author: Tony Werten
Date: 12:34:38 12/28/02
Go up one level in this thread
On December 28, 2002 at 14:50:00, Russell Reagan wrote: >On December 28, 2002 at 14:01:24, Tony Werten wrote: > >>If a move is better than score it means it is somewhere between x and y ( >>probably between score and y ) and you have to check if this is true. > >Thanks Tony. Let me see if I understand now. > >In PVS, you search with a window of (alpha,alpha+1). If the score from that >search is in the range (alpha,beta) that means that move is better, and you have >to re-search to find out how much better. Almost. If the score returns alpha+1, it always means it's better. If this node was called itself with (alpha,alpha+1) then there is no score>alpha AND score<beta (hence zero window search), so no need to research. >This same concept applies at the root. >If you search with an aspiration window, and the score comes back between alpha >and beta, then you know that this move is better, but not how much better. >If >this happens in the middle of a search (like in PVS) you have to re-search. But >if this happens at the root, you can set that as your new "move to play", even >though you don't know how much better the move is until you finish re-searching. >The advantage is that you will play the "better" move if the re-search doesn't >finish in time. Well, not completely. It happens quite often that the report "better move" is not correct. At the root, you have to check with an open window to make sure. > >Or more generally: If you search with an aspiration window, and the score is >between alpha and beta, you must re-search. The exception is at the root where >you could play the move, knowing it is better than what you had, without having >to re-search. > >Do I understand correctly? Yes, with the upper small correction. To look at it another way. When you get the report "better move" anywhere in the tree, you go up to the first node where (beta-alfa>1) and get the exact score (so research). Then you go down again with zero-window. Tony > >Russell
This page took 0 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.