Global State

Last updated on 16th July 2024

The global state is an object that can be read by all agents.

If your model doesn't need to make use of a global state, Agents and the AgentBasedModel need to be typed as GlobalState in order for the model to compile.

Generifying agents with default GlobalState (java)

public class MyModel extends AgentBasedModel<GlobalState> {}

public static final class MyAgent extends Agent<GlobalState> {}

If you have some global state to be shared across the system, create a Globals class that extends GlobalState, and pass as a type to the AgentBasedModel. Agents will now need to be typed as Globals in order to access values inside Globals.

Creating a custom global object(java)

public class MyModel extends AgentBasedModel<MyModel.Globals> {
  public static final class Globals extends GlobalState {
     public float preference = 0.35f;
  }
}
public static final class MyAgent extends Agent<Globals> {}

To get the globals values and update them from inside the model setup() or step().

Accessing a global from model (java)

public class MyModel extends AgentBasedModel<MyModel.Globals> {
  public static final class Globals extends GlobalState {
    float fillFactor = 0.25f;
  }

  public void setup() {
    getGlobals().fillFactor = 0.5;
    super.setup();
  }
}

To get the globals values from inside the Agents

Accessing a global from and agent (java)

public static final class MyAgent extends Agent<Globals> {
   private void updateHappiness() {
     long similar = // calculate similar
     long total = // calculate total

     float preference = getGlobals().preference;
     this.person.happy = (float) similar / total > preference;
    }
 }

Important

Do not attempt to change the values of globals from inside Agents. The results may not be as expected as all actions for all agents happen in parallel.

Annotations and Global State

Annotations can be used inside the global state to set the values of the global state from the console, or to report a global state value.

Annotating a global variable(java)

public static final class Globals extends GlobalState {
   @Input public float preference = 0.35f;
}

Reporting Deployment