Author: Robert Hyatt
Date: 21:44:53 01/21/02
Go up one level in this thread
On January 21, 2002 at 14:27:34, David Rasmussen wrote: >On January 21, 2002 at 10:41:39, Robert Hyatt wrote: > >> >>You have to do two things: >> >>1. If you get a fail high at the root on a zero-width window (any move after >>the first move should be searched with a zero-width window) you can't trust it >>unless you re-search it with a bigger beta bound and make _sure_ that it doesn't >>then fail low. Such fail-high (zero window) fail-low (non-zero window) is an >>artifact of null-move and if you play such a fail high move even if it fails low >>on the re-search, you will die... >> > >If you mean, do I count value >= alpha+1 from zero-window search as a fail high, >then no. In that case, I research with the original alpha;beta window. Isn't >that ok? > What if you run out of time? You failed high on the null-window search. You started a new search with a wider window and time expired. Do you play the fail-high move or stick with the previous best move? I stick with the last verified move. Unless I fail high a second time which means the original aspiration window was too small and I am now going to +infinity. I trust the second fail high but not the first. >>2. If you get a fail high at the root on the zero-width window, and when you >>re-search you get another fail high on the original aspiration window, or you >>get a true score, then you can trust it. >> > >That's what I'm doing now, I think. > >>Case 1 is the killer although it doesn't happen every move, once in a game >>is more than enough. > >I'm sure. > >But when I posted, I was really talking about the case where you search with an >aspiration window, and then you get a fail high with value v. You search with a >new aspiration windows (in my case [v;MATE]), but then the search turns out to >find nothing. The fail high was false. How do I avoid that? > You just take that and go with it. It is easy to see how it can happen, where a hash entry says "score >= XXX" which will cause a fail high, but now you can't use that and if you can't see it with a search, you are now forced to fail low. But the fail high was _right_. It is that PVS null-window fail high that can't be trusted at all... >/David
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.