Forum Archive :
GNU Backgammon
I have a question concerning gnubg's analysis' ply level. I suppose it
is a general question that affects all bots, not just gnubg.
Reading posts on this NG, I've heard several times that gnubg's analysis
at 1-ply can be unfortunate at times and produce not so good results and
that one should rather use 2ply beacuse it gives much more accurate
results, which I do anyway. Further, I got the impression that odd-ply
analysis is not so good as even-ply, so I ask if there is any truth to
this and briefly how to explain this.
For instance, I usually analyse using gnubg's preset worldclass++
setting i.e on 2-ply. On some moves where I have a dispute with gnubg's
2-ply analysis, I evaluate the top moves or the cube decision at 3-ply
and see how my play ranks there. Sometimes I would go up to 4-ply,
although very rarely because that takes too long. I notice quite often
that the even-ply analysis are usually close and agree among each other
but they disagree with the odd-ply analysis i.e 2 and 4 ply would agree
but 3ply gives different results. Actually I noticed that quite often
when going through some examples of Robertie's Advanced Backgammon.
So, I guess the question is what is behind this odd-ply and even-ply
analysis level and which should I trust more and what pitfalls are there
when using either one.
thx!
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Gary Wong writes:
You are quite right that several types of positions exist where odd- and
even-ply evaluations disagree. Unfortunately, there is no general
procedure to decide which one to trust more; in fact, if the two disagree
by a significant amount, then that is a good indication that you should
be suspicious of both.
A long time ago, I found some results which made me suspect that 1-ply
evaluations were _worse_ than 0-ply for an old version of gnubg.
However, a subsequent longer run of tens of thousand of games
indicated that 1-ply was indeed stronger by a small but significant
amount (+0.012ppg cubeless, +/-0.004). On average, you can expect n+1
ply evaluations to be more accurate than n-ply evaluations; there is
nothing to suggest that even or odd n is better overall.
Cheers,
Gary.
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GNU Backgammon
- Analyzing GamesGrid matches (Roy Passfield, Dec 2001)
- Batch analysis tool (Øystein Johansen, June 2004)
- Cache size (Ned Cross+, Mar 2004)
- 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)
- Error rates: Gnu vs. Snowie (Raccoon, Mar 2006)
- 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)
- 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)
- 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)
- JSD's and confidence intervals (Daniel Murphy+, Jan 2005)
- Logging rollouts (Øystein Johansen, Oct 2004)
- Luck rate (Kees van den Doel+, May 2002)
- MWC versus Equity (EMG) (Ken+, Apr 2005)
- Manually entering first roll (Andreas Graf+, Apr 2005)
- Match equity tables (Raccoon, July 2005)
- Personal reflections (Louis Nardy Pillards, Sept 2002)
- Playing two computers against each other (Stanley E. Richards+, Mar 2008)
- Python scripting (Øystein Johansen+, Nov 2004)
- Quasi-random dice in rollouts (Ian Shaw, Mar 2004)
- 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)
- Restarting a rollout with different settings (Robert-Jan Veldhuizen, Apr 2004)
- Rollout settings (geoff arnold+, Apr 2007)
- Rollout settings (Stick+, Nov 2005)
- Rollout settings (Robert-Jan Veldhuizen, Mar 2004)
- Rollout settings (Ian Dunstan, Aug 2003)
- Rollout settings for the impatient (Robert-Jan Veldhuizen, June 2004)
- Running rollouts in background (Bruce+, Apr 2004)
- Saving rollout results from command-line interface (Jeremy Bagai+, Apr 2006)
- Saving rollouts (Mislav Radica+, May 2006)
- 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)
- What's GNU? (Gary Wong, Oct 2001)
- Which player is player 0? (Neil Kazaross+, Oct 2004)
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