Computer Chess Club Archives


Search

Terms

Messages

Subject: Re: Fruit - Question for Fabien

Author: Dan Honeycutt

Date: 09:10:02 03/12/04

Go up one level in this thread


On March 11, 2004 at 12:56:37, Fabien Letouzey wrote:

>
>On March 11, 2004 at 12:40:40, Dan Honeycutt wrote:
>
>>Can you explain your statement in an earlier thread "I never "hash cut" at PV
>>nodes (I only read the best move) so that my PV is never truncated."
>
>>At the start of each iteration i save the pv from the previous iteration and set
>>a flag.  while the flag lasts i use it to order moves and avoid hash cuts.
>>however, once the old pv plays out and the flag is cleared any new pv is
>>(likely) truncated.  do you have a way around that?
>
>So you flag the "leftmost branch" only right?  If one of your PV move is wrong
>(another one is found to be better), you "lose" the flag, is that it?  This
>reminds me of a non well-known algorithm called P-alpha-beta which is a hybrid
>between alpha-beta and PVS.  It is interesting in itself, but I disgress ...
>
>If you use a PVS variant, a common way of knowing that the current node type is
>"PV node" is to test if (beta!=alpha+1) (non-null window, this assumes you are
>using PVS).  If you never apply hash cuts at those nodes, your PV should always
>be complete.
>
>Note that this may be affected by "window reductions" (aspiration, "shrunk"
>window after a re-search failed high, ...).
>
>But the short answer is (beta!=alpha+1) :)  If you don't use PVS, then you can't
>predict in advance if the current node is going to be PV or not of course :)
>
>Maybe I did not understand your question correctly, don't hesitate asking for
>more precision.
>
>Fabien.

You all are a bit over my head but thanks Fabian and others.  I lose the flag
right away.  I simply follow the pv from the previous iteration (avoiding hash
cuts) till it runs out then the search goes it's merry way.  the pv looks like

iteration  pv moves
  :
  2        a b
  3        a b c
  3        d e f
  4        d e f g
  4        h

everything looks like i think it should till that 1 move pv pops out.  if i read
Bob's reply right this is normal, don't worry about it.

i am using PVS so the beta!=alpha+1 gives me something to tinker with.

thanks again
Dan H.



This page took 0.05 seconds to execute

Last modified: Thu, 07 Jul 11 08:48:38 -0700

Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.