Computer Chess Club Archives




Subject: Re: An MTD(f) question about NULL MOVE searching

Author: Vasik Rajlich

Date: 03:33:20 07/16/04

Go up one level in this thread

On July 16, 2004 at 03:35:37, Tord Romstad wrote:

>On July 16, 2004 at 02:02:10, Dann Corbit wrote:
>>What are the tricks necessary to get NULL MOVE successfully integrated into an
>>MTD(f) search?
>>Is there anything special that needs to happen?
>In theory, there is a problem with search inconsitencies.  In practise, I've
>that it isn't that bad.  I don't use any tricks at all.  A standard recursive
>move search works fine.

There is one interesting caveat in comparison to PVS. A PVS engine has the
choice to treat null move as any normal move, or to require that the null move
fails high. (ie within bounds, but not fail high, is not enough) The latter is
somewhat logical, and IIRC this is what Crafty does.

An MTD (f) engine must treat a null move as a normal move. I couldn't come up
with a way to circumvent this restriction. It seems to be an inherent
restriction of the MTD (f) search.

Another way to look at this: an MTD (f) engine must accept null moves along the
"pv", where "pv" is defined as following the fail-high moves, and
highest-scoring fail-low moves.


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.