Computer Chess Club Archives


Search

Terms

Messages

Subject: fail low question

Author: Reinhold Gellner

Date: 23:43:12 10/22/97


Doing a zero-window search, fail high moves have to be re-searched.
Usually I do it with

actual_value = -re_search( -beta, -actual_value );

However, as extensions or just move ordering changes, the re_search is
not neccessarily the same and may result in a fail low! That is,
actual_value is now below the former actual_value but >= alpha.

I think this is a common problem. I have three solutions:

1. ignore this fail low at all
2. do another re_search: actual_value = -re_search( -actual_value,
-alpha)
3. do the initial re_search an open window:
   actual_value = - re_search( -beta, -alpha );

ad 1) this version may be dangerous in blitz games and of no importance
in tournament games, resulting in a speed up.

ad 2) the second search may now fail high again, or even oscillate,
resulting in an eternal loop.

ad 3) this safe approach seems to significantly increase the effective
branching factor.

How do you solve this problem?

Reinhold



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.