Variables

Defining a Process > Defining Model Elements and Advanced Elements > Variables

Variables

Variables are of two types: global and local. Global variables are place holders defined by the user to represent changing numeric values. Local variables are place holders which are available only within the logic that declared them. Variables can contain either Real or Integer numbers, and are typically used for decision making or recording information.

A global variable can be referenced anywhere numeric expressions are allowed in a model. If a variable is needed only in a single block of logic, it is easier to define a local variable right inside the logic block.

Global variables are defined in the Model Elements dialog, and have the following options:

Name The name of the variable. Double click on an existing name to change the name.
Type The type of variable, real or integer.
Initial Value The initial value of the variable to be assigned at the start of the simulation. By default, initial values are 0, but can be changed to whatever value you want.
Statistics You can choose to collect no statistics, time-weighted statistics, or observation based statistics for the variable.

Time-Weighted Statistics Collects total changes, average minutes per change, current value, average value, and time-weighted statistics of the variable. The example below illustrates the calculation of time-weighted statistics for variables:

Variable Observation Record	Value	Time in Hours
Observation 1 Observation 2 Observation 3 Observation 4	6 5 6 5	1 2 3 4
Total	22	10

Time-weighted collects information on the percentage of time the variable was at a specific value. As shown in the above table, the average value of the variable is:

(6 x 1) + (6 x 3) + (5 x 2) + (5 x 4) = 5.4

Observation Based Statistics Collects information on the number of times the variable changed to a specific value. As shown in the previous table, the value of the variable is 6, then, 5, then 6, and then 5. The average would simply be as shown below:

6 + 5 + 6 + 5 = 5.5

Graphic The variable's graphic appears as a counter in the layout, and displays the change in the variable's value during simulation. If you delete the variable's graphic from the layout, the variable itself will not be deleted, the Graphic option will just become unselected. Press the Delete key while a record is highlighted in the list of variables to delete variables from the model.

Local variables are defined with the Local Variable statement in the Logic Builder.