Getting started with GNUBG – A Guided Tour Part 3
by Robert-Jan Veldhuizen

Reviewing an analyzed match
To see GNUBG's analysis of individual moves, you first have to open the analysis section in the main window. Go to the "View" menu and check "Analysis". Find the games and moves you are interested in with the game record buttons and drop-down list. You should see something like this:

missing image!

The analysis section is a lot like the "Hint" window. You can click the "Details" button to toggle between an equity only view, or a two lines equity plus w/g/bg breakdown view as in the picture above.

In the game record section, the biggest errors will be marked as follows:

  • ?! and Green (checker) or Grey (cube): doubtful (default: 0.04-0.08 error)
  • ? and Blue (checker) or Yellow (cube): bad (default: 0.08-0.16 error)
  • ?? and Red (checker) or Magenta (cube): very bad (default: >0.16 error)

Additionally, very lucky dice rolls will be shown in bold, very unlucky rolls in italics.

The three boxes in the middle, at the top of the analysis section are also used to give labels to your play or cube errors and (very) (un)lucky dice rolls. Below that, use the tabs "Checker play" and "Cube decision" to see GNUBG's analysis results for each.

Just as with the "Hint" window, the analysis section provides many buttons to re-evaluate or roll out selected candidate moves, toggle between MWC/EMG or get more information from the temperature map, etc. Additionally, you can get lots of informations from various items in the "Analysis" menu. I will discuss these more advanced features in a later article, some of them require lots of settings and there are many issues to consider. You can have a look at what's all possible with rollouts for instance, by clicking the "..." (settings) button next to the "Rollout" button.

The quickest way to get some more information about a position that interests you, is to do a higher-ply evaluation, using the numbered buttons. When you're considering a move, it is interesting to see if 3-ply and 4-ply (slow!) evaluations support the 2-ply analysis. If they don't, then maybe GNUBG has some troubles with the position and a rollout is warranted. When you're considering a cube decision, remember that for these, GNUBG is often more reliable at even-ply than at odd-ply, so 2-ply and 4-ply are usually better indicators than 3-ply. Especially for cube decisions though, a rollout can give much better information than an evaluation.

Setting up a position
If you see an interesting position somewhere on the web or in a book, you might want to enter it in GNUBG and perform an analysis. To do this, start a new game, match or session with GNUBG and check "Manual dice" (It is best to make sure both players are set to "Human", you can change that with the "Players" settings). It doesn't matter what you enter here, just get some game going. Now, there is a very quick way to get the right position and match info, if you have a PositionID (and MatchID). Look for them in newsgroups and forums where people use GNUBG. Just enter both codes in the boxes at the top, press enter and there you are.

If you're not lucky enough to have these ID's, you will have to set things up manually. Click the "Edit" button at the top. Start by entering the information at the bottom of the window: player's names and most importantly, the matchlength (Zero means a money game session!), matchscore and whether it's the Crawford game or not. Set whose turn it is by clicking on the appropriate checker, that is in front of the player's names. To change the cube value and position, click on it. A window with all cube possibilities opens, click on the one you want. The number should face the side who owns the cube, or be sideways for a center cube.

Then, set up the checkers. This is quite intuitive but might take a bit of practice at first. Just experiment with it. Click in one of the trays on the left or right side of the board to either put all checkers off the board, or get to the starting position. You can add checkers to a point by clicking on it; left-click is bottom player, right click is top player. Move vertically on a point to change the number of checkers you get with a click. You can also use this to put checkers on the bar. Click on the border just below a point to clear it (checkers will move to the bear-off tray). You can also drag a checker, by holding down the Ctrl-key on your keyboard, then keep your left-mouse button down while moving a checker around. Realize that GNUBG will not allow more than 15 checkers on the board, so you might have to empty a point first to add checkers to another point.

When you're done, don't forget to click on the "Edit" button again. Now you can either click to roll the dice (manually) and play one of the candidate moves for a checker play problem; or make a cube action like double, take for a cube decision problem.

To analyze the problem, go to the relevant move in the game record (you probably have to skip back one or two clicks). Then use "Analyze move" from the Analysis menu. Results will appear in the analysis section; from there you can do further analysis like rollouts. To save results, save as a game or match file (*.sgf) so that the analysis will be saved too (do not use "Save as position" for this, it won't save the analysis).

End of Tour
For now, this concludes the introduction to GNUBG's most basic features and peculiarities. I hope this will help you get started working with GNUBG and I encourage you to take a look at all the other features the program has to offer. Some of them may be self-explaining, others are quite complicated. You can help me improve this GNUBG Tour by writing your comments, problems and suggestions to the email address below. I am also very interested in hearing which topics you are most interested in for either an extension to this Tour or a future article or tutorial.

Useful links and references
There is quite a lot of documentation about GNUBG on the web, so it can be rewarding to look around a bit. Realize that as GNUBG is a project under continuous development and run by volunteers; parts of it may be outdated or incomplete. Here are a few useful links:

For bug reports, suggestions or questions on GNU Backgammon you can contact the developers on the GNUBG mailing list at bug-gnubg AT

A big thank you should go to the development team of GNUBG, of course:

  • Joseph Heled
  • Øystein Johansen
  • Jonathan Kinsey
  • David Montgomery
  • Jim Segrave
  • Jørn Thyssen
  • Gary Wong

Further credit goes to Albert Silver for providing the first comprehensive, excellent tutorial on GNUBG; Achim Müller for writing and maintaining large parts of the Documentation and FAQ for GNUBG and to the many other people that contributed in any form to the GNUBG project!

Copyright © 2006 by and Robert-Jan Veldhuizen

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