General concepts#
General layout of the main window#
The frame presenting a game consists of a single main panel, which displays the game graphically; in this case, showing the game tree of a simple one-card poker game. Note that where applicable, information is color-coded to match the colors assigned to the players: Fred’s moves and payoffs are presented in red, and Alice’s in blue. Players are added, removed, reordered, renamed, and recolored on the Players page of the Game properties dialog (), in the same way as a player’s strategies are edited on the Edit strategies dialog (see Adding, removing, and reordering strategies): each player has a text field for its name, a color swatch beside it that opens a color picker when clicked, and ↑/↓/✕ buttons to reorder or remove it. A player can’t be removed if it has decisions in the game, or more than one strategy in the game’s strategic representation; its ✕ button is disabled, with a tooltip explaining why.
Two additional panels are available. Selecting toggles the display of an additional toolbar across the top of the window. This toolbar controls the indication and elimination of actions or strategies that are dominated. The use of this toolbar is discussed in Investigating dominated strategies.
Selecting , or clicking the show profiles icon on the toolbar, toggles the display of the list of computed strategy profiles on the game. More on the way the interface handles the computation of Nash equilibria and other kinds of strategy profiles is presented in Computing Nash equilibria.
Payoffs and probabilities in Gambit#
Gambit stores all payoffs in games in an arbitrary-precision format. Payoffs may be entered as decimal numbers with arbitrarily many decimal places. In addition, Gambit supports representing payoffs using rational numbers. So, for example, in any place in which a payoff may appear, either an outcome of an extensive game or a payoff entry in a strategic game, the payoff one-tenth may be entered either as .1 or 1/10. The advantage of this format is that, in certain circumstances, Gambit may be able to compute equilibria exactly; see Computing Nash equilibria for how this interacts with the display of computed profiles.
A word about file formats#
The graphical interface manipulates several different file formats for representing games. This section gives a quick overview of those formats.
Gambit has for many years supported two file formats for representing games, one for extensive games (typically using the filename extension .efg) and one for strategic games (typically using the filename extension .nfg). These file formats are recognized by all Gambit versions dating back to release 0.94 in 1995. (Users interested in the details of these file formats can consult Game representation formats for more information.)
The graphical interface reads and writes an extended format, referred to as a “Gambit workspace”. This stores not only the representation of the game, but also additional information, including parameters for laying out the game tree, the colors assigned to players, any equilibria or other analysis done on the game, and so forth. So, for example, the workspace file can be used to store the analysis of a game and then return to it. These files by convention end in the extension .gbt. The graphical interface will read files in all three formats: .gbt, .efg, and .nfg.