Author: Robert Hyatt
Date: 07:24:10 12/31/00
Go up one level in this thread
On December 31, 2000 at 02:37:23, Steve Maughan wrote: >Bob, > > >>>Is it valid to raise the value of Alpha when the depth is sufficient and the >>>lowerbound is greater than Alpha? What happens to the PV? I'm just cutting it >>>off at the moment (i.e. PVLength := Ply). >> >> >>Why bother the PV? You are simply altering the bound. The PV should not be >>affected by this at all... > >Surely at least when alpha is raised this is equivalent to finding a new best >move and hence the PV needs to be cut off? I don't think so. I don't do this in Crafty, yet I raise alpha and lower beta just as you do. All the hash entry says is "this position should have a higher alpha bound (or lower beta bound)..." but it says nothing at all about a PV since you still have to keep searching... > >The other post says that Beta can never be adjusted and this does sound right. >I'm having difficulty getting my head round what it actually means to lower beta >(apart from just narrowing the search). I see no reason beta can't be changed if alpha can. These are just _bounds_ on the reasonable values for the position. Lowering beta simply means that you know, from a prior search, that the value can not exceed the value of beta stored in the hash table, which is a lower bound than the one you are currently using. Improving the beta value could/should reduce the size of the tree. It should _not_ influence the PV in any way if it is done correctly. > >Steve
This page took 0.01 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.