GNU Backgammon

Forum Archive : GNU Backgammon

Setting skill level

From:   Jim Segrave
Date:   29 April 2004
Subject:   Re: Quick Question on GNU
Google:   c6q9ie$71c$

> I recently downloaded GNU but haven't gone through all the details of
> how to adjust the difficulty setting of the computer (for lack of a
> better term).  I'm still not familiar with all the computer terms
> associated with these settings (ply and all that).  If I want GNU to
> play the best game so that I can compare the hints to my moves and be
> sure I am doing the best thing, what should I change, if anything, to
> make sure I'm at the right "difficulty" level.  In Jellyfish I just set
> it at level 7, but I'm not sure what the comparable thing on GNU is.

There are several places in gnubg where you can adjust either it's
skill at playing or the quality of it's hints and analysis:

Playing skill:
   Settings->Players->Player 0 - choose Supremo or World Class. Gnubg
      will take longer choosing its moves, but they will be *very*
      strong. At this setting, it is much stronger than Jellyfish
   level 7.

   Settings->Evalutation - choose Supremo or World Class if you want
      hints to be very accurate, but, like the playing skill settting,
      you may find that it can take as long as 15 seconds to get an
      answer on a 1GHz PC. Expert will be very fast, but for some
      positions where you need to consider what your opponent may do
      on his roll and how you will follow it up, the results will be
      less accurate. A wild guess would be somwhere around 2 or 3
      percent of the time, World Class or stronger settings would give
      a different best move and maybe less than 1/2 percent of the
      time, the Expert result would be seriously wrong.

   Settings->Analysis - these settings are used by the Analyse
      Move/Game/Match or Session command. Note that this is totally
      different to what is used in the Hint command, which uses the
      above settings. You probably want at least World Class here. My
      experience on a 700MHz PC is that a 7 point match takes about 15
      to 20 minutes to analyse on the Supremo settings. But the
      results tend to be very accurate.

   Settings->Rollouts->General Settings: tick the boxes for 'Cube
     decisions use same settings same as chequer play' and 'Use same
     settings for both players'

   Settings->Rollouts->First Play Both - select Expert here (this is
      my opinion). When doing rollouts, most of the time Expert play
      will be more than strong enough if you do say 1296 trials with
      no truncation. The rolout function has an enormous number of
      options, most of which are only useful when trying to
      investigate special positions. The simple expert setting for
      both players is probably more accurate than any of the Analysis
      functions. The downside is that rolling out 1296 trials of an
      early move in a game can take a couple of hours. On World Class
      or Supremo rollout settings, it can take more than 24 hours of
      computing time.

As a footnote - a ply is considered to be one turn by a player. Gnubg
differs from some other software, notably Snowie in that gnubg zero
ply is the same as Snowie 1 ply (perhaps gnubg developers count from
0, Snowie developers count from 1).

For gnubg, a 0 ply evaluation of a move would be done by:

Build a list of all legal moves.  For each move, take the resulting
board position and use the neural net to estimate the expeted
percentage of wins/gammons/backgammons/losses/gammon losses/backgammon
losses. Rank the moves based on this evaluation.

For one ply, after doing the above step, gnubg chooses the best n
moves (where n is set by the move filters). For each one, it takes the
resulting position for that move and goes through all 21 possible dice
rolls for the opponent. From these results, it works out the average
expectation for the initial move and ranks them. This is the same as
Snowie 2 ply. You can think of it as asking "what's my best move if I
also consider every possible dice roll and move my opponent might

For 2 ply (Snowie 3 ply), a similar process is done, but this time,
not only are the opponents possible moves considered, but, for each of
these, the player on roll's next move will be considered as well.

For a single move, on average there are about 20 legal moves to

When doing a one ply analysis/evaluation, for the top n moves (from
the move filter, gnubg needs to consider 21 rolls by the opponent, 20
and possible legal moves per roll) = 420 positions to evaluate.

Every additonal ply will multiply the previous number of evaluations
by about 400 odd, which explains the huge difference in playing
speed/analysis speed between 0 ply and 2 ply settings. I don't think
many people would enjoy playing against gnubg at 3 ply settings, where
moves could take minutes to be selected. It's also not clear that
using much deeper lookahead acctually gains a lot in terms of playing
strength - if you really need better answers than 2 ply, rollouts are
probably a lot better.

Jim Segrave 
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GNU Backgammon

Analyzing GamesGrid matches  (Roy Passfield, Dec 2001) 
Batch analysis tool  (Øystein Johansen, June 2004)  [GammOnLine forum]
Cache size  (Ned Cross+, Mar 2004)  [GammOnLine forum]
Compiling for Windows  (Øystein Johansen, Jan 2002) 
Edit mode removing checker from bar  (Scott Steiner+, May 2003) 
Entering an annotated match  (Albert Silver, Dec 2003)  [GammOnLine forum]
Error rates: Gnu vs. Snowie  (Raccoon, Mar 2006)  [GammOnLine forum]
Even-ply/odd-ply effect  (Raccoon, Nov 2004) 
Even-ply/odd-ply effect  (Tom Keith+, Oct 2003) 
Even-ply/odd-ply effect  (Scott Steiner+, Dec 2002) 
Filter settings  (Robert-Jan Veldhuizen, Nov 2004)  [GammOnLine forum]
Gnu 0.13 versus Jellyfish and Snowie  (Torsten Schoop, Aug 2003) 
Gnu 0.13 vs. Snowie 4  (Albert Silver, June 2003) 
Gnu 0.14 vs. Jellyfish  (Michael Howard+, July 2003) 
Gnu versus Snowie and Jellyfish  (Michael Depreli, Oct 2005) 
How luck factor is calculated  (Gregg Cattanach, Aug 2002) 
How rollouts work  (Gary Wong, July 1999) 
How to enter an illegal move  (Øystein Johansen, Aug 2003)  [GammOnLine forum]
Importing .gam files  (PAR+, Mar 2005) 
Importing PartyGammon matches  (rew+, July 2006) 
Improving your game using GnuBG  (D.U.G.+, Nov 2002) 
Installing on Windows  (maareyes, Oct 2001) 
Interpreting JSD's  (Adrian Wright+, Feb 2005)  [GammOnLine forum]
JSD's and confidence intervals  (Daniel Murphy+, Jan 2005) 
Logging rollouts  (Øystein Johansen, Oct 2004)  [GammOnLine forum]
Luck rate  (Kees van den Doel+, May 2002) 
MWC versus Equity (EMG)  (Ken+, Apr 2005)  [GammOnLine forum]
Manually entering first roll  (Andreas Graf+, Apr 2005) 
Match equity tables  (Raccoon, July 2005)  [GammOnLine forum]
Personal reflections  (Louis Nardy Pillards, Sept 2002) 
Playing two computers against each other  (Stanley E. Richards+, Mar 2008)  [GammOnLine forum]
Python scripting  (Øystein Johansen+, Nov 2004) 
Quasi-random dice in rollouts  (Ian Shaw, Mar 2004)  [GammOnLine forum]
Question marks in game list  (Jim Segrave, July 2005) 
Questions and answers  (Jim Segrave+, Jan 2003) 
Questions and answers  (Jørn Thyssen, Aug 2002) 
Restarting a rollout with different settings  (Jim Segrave, Apr 2005)  [GammOnLine forum]
Restarting a rollout with different settings  (Robert-Jan Veldhuizen, Apr 2004)  [GammOnLine forum]
Rollout settings  (geoff arnold+, Apr 2007) 
Rollout settings  (Stick+, Nov 2005)  [GammOnLine forum]
Rollout settings  (Robert-Jan Veldhuizen, Mar 2004)  [GammOnLine forum]
Rollout settings  (Ian Dunstan, Aug 2003)  [GammOnLine forum]
Rollout settings for the impatient  (Robert-Jan Veldhuizen, June 2004)  [GammOnLine forum]
Running rollouts in background  (Bruce+, Apr 2004)  [GammOnLine forum]
Saving rollout results from command-line interface  (Jeremy Bagai+, Apr 2006)  [GammOnLine forum]
Saving rollouts  (Mislav Radica+, May 2006)  [GammOnLine forum]
Setting GnuBG's playing strength  (JP White, Sept 2001) 
Setting skill level  (Jim Segrave, Apr 2004) 
Setting up and saving a rollout  (Albert Silver, Dec 2003)  [GammOnLine forum]
What's GNU?  (Gary Wong, Oct 2001) 
Which player is player 0?  (Neil Kazaross+, Oct 2004)  [GammOnLine forum]

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