Author: Dieter Buerssner
Date: 12:06:55 07/12/03
Go up one level in this thread
On July 12, 2003 at 14:43:52, Heiner Marxen wrote: >On July 12, 2003 at 14:13:25, Omid David Tabibi wrote: > >>Hi, >> >>After a few days of rewriting large parts of my program's code, to my surprise I >>found out that: >> >>if (value >= beta) >> return beta; > >The classic version. > >>and >> >>if (value >= beta) >> return value; > >This variant is called "fail soft". When also additionally, you don't return alpha in fail low situations, but a best value. I actually wonder, if you have a classic fail hard search, and just change one line in search like above, can it change anything? The parent node could return alpha (not less). So did the child. Where can this value > beta come from? >The caller must be prepared to receive a value outside the alpha/beta window. > >>don't yield the very same result. > >The second version (fail soft) has the potential to generate better results, >sometimes. When these are reused via the TT, the rest may change. Yes. It might also influence move-ordering, for example when using some "mate killer heuristics". Additionally, for PVS combined with null move an aritifact can arise. With another bound in the research (which will be needed here), you might not fail high null move anymore (the original null move fail high was sort of bogus), and the whole normal search could show, that it would not result in a value as high as the value returned by the null move. Similar for other pruning techniques, and perhaps even extensions (when dependent on bounds). >>I've been trying to find the bug for the past 24 hours, without any success so >>far. Has anyone experienced this problem in the past?! Any ideas as to the >>possible source of the problem? >> >>Thanks. > >What is the problem? Good question. Many such things are just unavoidable for efficient search. Regards, Dieter
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.