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Subject: Re: Search behavior in a case of root fail high/low

Author: Tord Romstad

Date: 07:32:38 03/10/04

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On March 10, 2004 at 07:56:17, Sergei S. Markoff wrote:

>Hello!
>
>I think that there are a lot of ideas that can be used to reduce search tree,
>clever changing a window size of a root search.
>
>There are some weaknesses of MTD(f) or MTD(f)-like schemes that not allow to use
>this schemes by the most of engines. The first is very hard depending of hash
>storing/probing efficiency; the second - troubles with null-move. I tried
>something like MTD(f) before, including trying to determine move singularity in
>position (actually we don't need the exact score of move sometimes to make best
>move).

Hello Sergei,

My own engine is nowhere near as strong as SmarThink, but it tries to
implement some similar ideas.  In particular, I also use knowledge
extensively to guide the search, and like you I use techniques like
history based pruning and the Botvinnik-Markoff extension.

However, I do use MTD(f), and I am therefore interested in learning
more about the problems and weaknesses you mention above.  I agree
concerning the importance of the hash table, but I am not sure I
understand your problems with the null move.  Are you referring to
the search inconsistencies caused by trying the null move multiple
times in the same position but with different values of the search
bound, or were you thinking about some other kind of problem(s)?

I am mostly very happy about my MTD(f) search, and I think I would
need many months to write an equally efficient PVS search.  The only
problem I see is the uncomfortably high frequency of search
inconsistencies.

Tord



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