Computer Chess Club Archives


Search

Terms

Messages

Subject: Re: Failing low at the root

Author: Robert Hyatt

Date: 02:53:36 08/04/98

Go up one level in this thread


On August 03, 1998 at 14:33:17, Roberto Waldteufel wrote:

>
>Hi Bob,
>
>Maybe I am misunderstanding what happened, but something sounds a little strange
>here. When the search first finds that the pawn can't be held and fails low at
>the root, it gives you an upper bound on the position that is less than the
>value you previously used for beta by about the value of a pawn, so surely at
>this point you re-adjust the search window at the root to take account of this,
>so that when you re-search to depths 1,2 etc you do so with lower expectancy.
>The positions you reach in the researches should mostly have bounds stored from
>the search that failed low to start with, so I don't see why the search should
>keep failing repeatedly unless you hit hash records from lower depths (before
>the initial fail-low) and allow the lower depth re-searches to fail high and
>override your upper bound from the orriginal fail high, but could you not easily
>prevent this from happening by disabling the researching process until you had
>reached your previous depth again? I would be surprised if Schaeffer is
>recommending something as useless as you make it sound.
>
>Best wishes,
>Roberto

doesn't help, although I do this.  Because if you limit beta, and search from
iteration 1 again, but with alpha/beta centered on the expected window at the
fail low depth, the first move that fails high at ply=1, and one will fail high,
relaxes this.

The problem is that you filter new moves back up to depth=8, where the promptly
fail low.  But it takes time to filter them back up.  If you don't let the
fail-high happen on the re-searches at shallower depths, you may as well just
pick a move randomly to search, bcause *all* will fail high since it seems that
the pawn can be held until you reach the right depth.

Note that this was the only thing I looked at.  There were other positions where
it was also way slower...  but this caught my attention..



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.