Author: Bruce Moreland
Date: 09:17:37 01/22/98
Go up one level in this thread
On January 22, 1998 at 08:16:35, Robert Hyatt wrote: >On January 22, 1998 at 02:30:48, Bruce Moreland wrote: >>I don't know exactly why the PV (first) move takes so long to resolve, >>but I can guess. I think that it takes a while to resolve because the >>window is wide, and the value will probably be within the window. >> > >Think about ply=2. For a non-first move, you search one move there. >That >is enough to refute the ply=1 move. For the first move, you have to >search *every* ply=2 move since there is no bound to cut off against >yet. > >For the first move, as you advance down the left-side of the search >tree, >assuning it is drawn so you search left-to-right, *every* left-most node >must have every alternative searched. > >For non-first moves, in a perfectly ordered tree, every even-ply >position >only has to search one move. I want to point out that we aren't arguing, in case I am wrong and we really are. The fact that you are within the window is *why* you aren't cutting off, right? >>From experience it seems like you get a faster result if you have a >>narrow window and the move fails low. If someone wants to prove this, >>cool, there is probably an easy proof for the mathematically inclined. > > >this is written up in a technical report by Jonathan Schaeffer, and was >referred to as "the minimax wall". As long as alpha/beta are below the >true value of the search result, searches run like the blazes, because >the entire tree is searched as though it had *no* best move and >everything >at the root gets refuted by the first move at ply=2 and so forth for >all >even/odd plies. Do you mean instead that alpha and beta are *above* the true value of the search? bruce
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.