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Re: [Bug-gnubg] GnuBG

From: Philippe Michel
Subject: Re: [Bug-gnubg] GnuBG
Date: Sat, 24 Feb 2018 22:03:31 +0100
User-agent: Mutt/1.9.3 (2018-01-21)

On Sat, Feb 24, 2018 at 02:38:22AM +0400, gela devadze wrote:

>    When I am setting up a difficult of game on "Grand Master" mode, 
> that I am pressing button (CHANGE), after that I dont know how to set up
> movements layer.
> for example: - 1ply - 2ply - 3ply - 4ply.

I don't see a "change" button, I suppose you mean "modify" in the Move 
filter part of the settings (or use another language than the default).

The play level setting is a combination of a lookahead depth (the plies 
number) and a move filter. The idea of the latter is that since 
lookahead takes time (every additional ply is about 21 times slower 
than the preceding one), moves are evaluated at 0-ply, without 
lookahead, first and only those that don't seem hopeless at this level 
are evaluated more thoroughly.

Grandmaster is 3 plies with a "large" move filter. The modify button 
shows what large means here. Since this is a 3 plies evaluation, the 
relevant part is the 3-ply one. It should have the 0-ply filter enabled 
with : "always accept 0 moves, accept extra 16 moves within 0.32"

That means that if one move is better than all other at 0-ply by at 
least 0.32, it will be played without further evaluations. If there are 
other choices worse by less than 0.32, up to 16 of them will be 
evaluated at a higher level.

The 1-ply filter is not enabled. That means all the up-to-16 moves above 
will pass it and be evaluated further.

The 2-ply filter is enabled with "always accept 0 moves, accept extra 4 
moves within 0.08" so the moves that have passed the earlier filters 
will be evaluated at 2-ply, if one seems better by at least 0.08 it will 
be played else up to 4 of them will be evaluated at 3-ply.

>    Please let me know how to set up everything on sure, that will work to
> set the proggrams gameplay mode maximally difficult.

The most important factor for the program strength is the plies number 
but as a sparring partner it doesn't make a big difference. O-ply 
(expert) is already stronger on average than the best human players but 
occasionally makes obvious errors. 2-ply and 3-ply (world class to 
grandmaster) make less such errors but if you didn't know which setting 
is in use you probably wouldn't be able to guess against which one you 
were playing. 4-ply is probably too slow to play against but can be used 
to analyse positions or matches.

The move filters are mostly a trick to have faster evaluations. When 
there are many plausible candidate moves, like playing small doublets in 
some cases, a larger filter may find a better move than a narrower one 
but these cases will be rare. On the other hand, if the speed is still 
fine with you, it doesn't hurt to do so.

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