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AnyLogic V User’s Manual

4.2 Equations

You can define a set of equations to describe continuous changes of variables over time. Thus you can define continuous time object behavior. See Chapter 5, “Equations” to know how to define equations.

An equation can be of three types:

•Differential equation (see section 5.1.1.1, “Differential equations”)

•Algebraic equation (see section 5.1.1.2, “Algebraic equations”)

•Formula (see section 5.1.1.3, “Formulas”)

You can define equations for a set of variables, maybe across several active objects.

AnyLogic supports matrices and hyper-arrays as well as primitive types in equations, see Chapter 6, “Matrices and hyper-arrays”.

4.3 Variable sharing

Variables can be shared with other active objects. Shared variables will have the same value at any moment of time; i.e., changes of one variable will be immediately propagated to another variable. This provides for continuous and/or discrete time object interaction.

Only the variables of compatible types can be connected.

To establish variable sharing, you should connect the respective variables (see section 4.3.2, “Connecting variables”). You can connect:

•interface variables of two encapsulated objects;

•either state or interface variable of a container object with an interface variable of an encapsulated object.

Connect variable of encapsulated object with an interface variable of the container object if you need to share it with container object neighborhood. Otherwise, if you need to share it only with a container object, use state variable.

AnyLogic V User’s Manual

Figure 34. Connection of variables

Variable change is propagated according to the well-defined set of rules (in Figure 34 directions of variable propagation are shown with arrows).

•When variables of two encapsulated objects are connected, output variable change is propagated to input variable.

•When variables of encapsulated and container objects are connected, the direction of variable change propagation depends on the dependency direction type of variable of encapsulated object:

•When it is the output variable, this variable change is propagated outside from the encapsulated object to the connected variable of the container object.

•Otherwise, if it is the input variable, the change is propagated from the container to the encapsulated object.

AnyLogic allows connection of several dependent variables to one output variable. But to prevent collisions, only one output variable can be connected to a dependent variable; otherwise, AnyLogic raises a compilation error. Some possible cases of invalid connection configurations are shown in Figure 35.

AnyLogic V User’s Manual

►To connect variables of encapsulated objects

1.Drag the variable of one encapsulated object onto the variable of another encapsulated object, or

Click the Connector toolbar button, click the first variable and then click the second variable, or

Choose Draw|Structure|Connector from the main menu, click the first variable and then click the second variable.

The connector linking two variables appears (see Figure 36).

Figure 36. Variables of encapsulated objects connected

Connecting variable of an encapsulated object with a variable of a container object

To establish continuous time interaction between the encapsulated object and the container active object you should connect a variable of an encapsulated object with a variable of the parent object.

Connect a variable of an encapsulated object with an interface variable if you want to establish interaction with parent object neighborhood. However, if you need only to propagate value of the variable of container object and encapsulated object, use a state variable.

►To connect a variable of an encapsulated object with a variable of a container object

1.Drag the variable of the encapsulated object onto the variable of the container object, or

Click the Connector toolbar button, click the first variable and then click the second variable, or

Choose Draw|Structure|Connector from the main menu, click the first variable and then click the second variable.

The connector linking two variables appears (see Figure 37).

AnyLogic V User’s Manual

In other words, use the connect()/disconnect() methods to connect or disconnect:

• Variables of encapsulated objects

Use the map()/unmap() methods to connect or disconnect:

• A variable of an encapsulated object with a variable of a container object

4.3.2.3 Using the methods connect()/disconnect()

Figure 38 shows the situation when the connect()/disconnect() methods are used.

Figure 38. Variables of encapsulated objects

Call the connect() method to connect varA with varB:

objectA._ref_varA.connect(objectB._ref_varB);

Call the disconnect() method to disconnect variables in the similar manner:

_ref_varA.disconnect(_ref_varB);

You can write this code anywhere you like in the parent active object class (objectC in the first case and objectA in the second one) code.

4.3.2.4 Using the methods map()/unmap()

The method map() is used for connecting variables located on the different levels of the containment hierarchy, namely a variable of an encapsulated object with a variable of a container object. Variables are disconnected by calling the unmap() method.

AnyLogic V User’s Manual

boolean hasInputConnection() – the method returns true if the input variable has an incoming connection and false otherwise.

4.4 Changing variables and reacting to their changes

You can also test variables continuously by specifying a Boolean expression as a trigger of a transition. As soon as the expression evaluates to true (even if this happens in the middle of a time step), the transition becomes enabled.

We recommend you to specify awaited conditions as triggers and not as guards. This is because guards are not tested during time steps.

In the example in Figure 41, the transition in object myObj2 fires as soon as the object myObj1 changes the value of x.

Figure 41. Responding to variable change (I)