Classes of variables and other objects

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Analytica User GuideExamining a ModelClasses of variables and other objects


The shape of a node indicates the class of the variable or other object:

Chapter1 11.png A rectangle depicts a decision variable — a quantity that the decision maker can control directly. For example, whether or not you take an umbrella to work is your decision. If you are bidding on a contract, it is your decision how much to bid.
Chapter1 12.png An oval depicts a chance variable — that is an uncertain quantity whose definition contains a probability distribution. For example, whether or not it will rain tomorrow is a chance variable (unless you are a rain god). And whether or not your bid is the winning bid is a chance variable in your model, although it is a decision variable for the person or organization requesting the bid.
Chapter1 13.png A hexagon depicts an objective variable — a quantity that evaluates the relative value, desirability, or utility of possible outcomes. In a decision model, you are trying to find the decision(s) that maximize (or minimize) the value of this node. Usually, a model contains only one objective.
Chapter1 14.png A rounded shape (with thin outline) depicts a general variable — a quantity that is not one of the above classes. It can be uncertain because it depends on one or more chance variables. Use this class initially if you’re not sure what kind of variable you want. You can change the class later when it becomes clearer.
Chapter1 15.png An hourglass shape depicts a constraint — a relationship utilized when solving constrained optimization problems in the Analytica Optimizer edition. The constraint node appears on the toolbar only when using Analytica Optimizer. Optimization is covered in the Optimizer user guide.
Chapter1 16.png A rounded node (with thick outline) depicts a module — that is, a collection of nodes organized as a diagram. Modules can themselves contain modules, creating a nested hierarchy.
Chapter1 17.png A parallelogram depicts an index variable. An index is used to define a dimension of an array. For example, Year is an index for an array containing the U.S. GNP for the past 20 years. Or Nation name is an index for an array of GNPs for a collection of nations. Indexes identify the row and column headers of a table, and the axes and key of a graph (see Introducing indexes and arrays.
Chapter1 18.png A trapezoid depicts a constant — that is, a variable whose value is fixed. A constant is not dependent on other variables, so it has no inputs. Examples of numerical constants are the atomic weight of oxygen (16) or the number of feet in a kilometer. It is clearer to define a constant for each such value you need in a model, so you can refer to them by name in each definition that uses it, rather than retyping the number each time.
Chapter1 19.png A shape like an arrow tail depicts a function. You can use existing functions from libraries, and define new functions to augment the functions provided in Analytica. See Building Functions and Libraries.
Chapter1 20.png This node is a button — when you click a button (in browse mode), it executes its script to per- form some useful action. You can use buttons with any edition of Analytica, but you need Analytica Enterprise or Optimizer to create a new button (see Creating buttons).

See Also


Diagram windowClasses of variables and other objectsSelecting nodes
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