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AnyLogic V User’s Manual

4. Variables

An active object can contain variables – entities that model data items (may be continuously changing over time). Variables are generally used to store the results of model simulation or to model some characteristics and parameters of objects, changing over time. During the model execution, variables are observable and changeable from the AnyLogic UI.

A variable can be of an arbitrary scalar type, a matrix of an arbitrary dimension, or a hyperarray – a multi-dimensional array of real numbers. This chapter describes scalar variables only. AnyLogic matrices and hyper-arrays are described in detail in Chapter 6, “Matrices and hyper-arrays”.

You can define a set of differential equations, algebraic equations, and formulas to describe continuous changes of variables over time. Thus you can define a continuous time object behavior. Modifying variables at runtime, you can adjust the model behavior.

Variables can be exposed to the active object interface and shared with other active objects. In this case, variable changes are immediately propagated to the dependent variable of another object. This provides for continuous and/or discrete time object interaction.

You can declare a Java member variable in the Additional class code code section of an active object class. Use member variables instead of variables if you just need a data item to be accessed only within an active object and only at discrete steps (i.e., it is neither shared with other objects nor changed continuously), and you do not want to observe or change that item during model execution.

Use a parameter (see Chapter 3, “Parameters”) instead of a variable if you just need to model some static parameter of an object changed only at particular moments of time (e.g., between model runs).

4.1 Defining a variable

Variables can be either internal (or state variables) or public (or interface variables). A state variable is only accessible from within the active object. An interface variable can be shared with other active objects.

AnyLogic V User’s Manual

You can simply change the accessibility status of the created variable.

►To make variable interface

1.On the structure diagram, drag the variable on the class border.

►To make variable state

1.On the structure diagram, drag the variable into the class border.

Interface variable is displayed on the structure diagram as a triangle. It can be either input (a triangle pointing inside the object) or output (a triangle pointing outside). The variable “direction” is significant in variable sharing – output variable changes will be propagated to the dependent input variable (see section 4.3, “Variable sharing” for the detailed description of variable sharing mechanism).

Once the new variable is created, you can specify the variable name in the text line editor opened on the right of the variable in the structure diagram.

Moving, copying and deleting variables

There are some common operations you can perform with variables on the structure diagram. You can copy, move and delete variables just as any other class elements. First, you should select the variable by clicking it.

►To move a variable

1.Drag the variable with the mouse or use arrow keys.

►To copy a variable

1.Ctrl-drag the variable.

►To delete a variable

1.Click the Delete toolbar button, or Choose Edit|Delete from the main menu, or

Right-click the variable and choose Delete from the popup menu, or Press Del.

AnyLogic V User’s Manual

►To initialize a scalar variable

1.Select the variable on the structure diagram.

2.Go to the Equation section of the Properties window.

3.Choose No equation from the Form drop-down list.

4.Specify the initial value of the variable in the Initial value edit box.

If an initial value is not specified, Java rules apply, for example a variable of type double is set to 0.

If a formula is defined for a variable, its initial value is calculated by this formula.

You cannot initialize input variable, since it commonly plays the role of dependent variable and its value depends on the value of connected output variable.

4.1.2Viewing and modifying scalar variables at runtime

AnyLogic supports variable modifying during the model simulation. You can change variables at runtime programmatically as well as from the AnyLogic viewer UI or from AnyLogic animation. If a variable is connected with another variable, the change is propagated in the shown “direction” of dependency, see section 4.3, “Variable sharing”. You can define a handler method that is invoked on a variable change.

4.1.2.1 Modifying variables from Model Viewer

►To modify a variable

1.Double-click the variable in the Model Explorer or on the animated structure diagram, or

Right-click the variable in the Model Explorer or on the animated structure diagram and choose Modify from the popup menu.

The Modify dialog box is displayed.

2.Type a new value in the Enter new value edit box.

AnyLogic V User’s Manual

3.If needed, specify the code to be executed when the user changes the control in the

Event handling code edit box.

4.1.2.4 Accessing and modifying variables from code

You can treat a variable as a regular Java object and modify, test, and use it at discrete event steps in any expressions — in actions of states, transitions, ports, timers, from threads, etc. A variable var1 of an active object can be accessed simply as the member variable var1.

For example, write the following code to modify and check varA variable value:

varA = 7;

traceln(“VarA = ” + varA);

4.1.2.5 Collecting dataset on a variable

AnyLogic supports collecting data on a variable during the model simulation in a dataset. You can visualize and export data collected in a dataset (see Chapter 17, “Collecting data and performing statistical analysis”).

Samples of variables can be collected automatically from the beginning of the simulation.

►To collect dataset automatically

1.Select the variable on the structure diagram.

2.In the Properties window, select the Auto collect dataset check box.

If auto collecting data is not set, data collecting starts only when and if the variable is added to a chart window.

4.1.2.6 Displaying plots of variables in Viewer

You can visualize variable changes during model simulation using AnyLogic chart windows. You can visualize data collected for variables in either explicitly created or automatically collected by AnyLogic datasets. See Chapter 17, “Collecting data and performing statistical analysis” for details on collecting and analyzing data.

AnyLogic V User’s Manual

►To add a variable to a chart window

1.Drag the variable from the Model Explorer onto the chart window.

►To set up the chart

1.Right-click the chart window and choose Chart Setup… from the popup menu. The Chart Setup dialog box is displayed (see Figure 33).

2.To add a variable to the chart, double-click the corresponding item in the Variables, parameters and datasets list.

3.To remove a variable from the chart, double-click the corresponding item in the

Axis Y list.

4.By default, Time is chosen in the Axis X list, that is the chart is timed. If you need to plot one variable against another variable, dataset, or parameter, make the chart phased. Set up the variable/dataset/parameter to be displayed on the x-axis by clicking the corresponding item in the Variables, parameters and datasets list, and then clicking the button to the left of the Axis X list. To make plot timed again, remove the variable/dataset/parameter item from the Axis Y list by double-clicking.

5.Click OK.