Repast Simphony: Scheduling a global behavior as Poisson process with random intervals

Question

I have a functioning model where I want to force a random agent to change state on a varying interval, modeled as a Poisson arrival process. I have set up a global behavior per the FAQ, by including a block in Build() that looks like this (where a and b are externalized in parameters.xml):

ISchedule schedule = RunEnvironment.getInstance().getCurrentSchedule();
ScheduleParameters arrival = ScheduleParameters.createPoissonProbabilityRepeating(a, b, 1);
schedule.schedule(arrival , this, "arrivalEvent");

Then I have a context method that looks like this:

public void arrivalEvent() {
    // stuff
    double tick = RunEnvironment.getInstance().getCurrentSchedule().getTickCount();
    System.out.println("New arrival on tick: " + tick);
}

This appears to work, except that it appears from the debug text to use the same value for b on all repeats. Is there a way for each repeat to use a new random draw? Or is there another (better) way to achieve this?

Answer 1

If you want b to vary each time, one way to do this is to reschedule arrivalEvent in arrivalEvent itself. The most legible way to do this is by implementing arrivalEvent as a class that implements IAction.

public class ArrivalEvent implements IAction {
    
    private Poisson poisson;
    
    public ArrivalEvent(Poisson poisson) {
        this.poisson = poisson;
    }
    
    public void execute() {
        // execute whatever the actual arrival event is
        
        
        // reschedule
        double next = poisson.nextDouble() + RunEnvironment.getInstance().getCurrentSchedule().getTickCount();
        RunEnvironment.getInstance().getCurrentSchedule().schedule(ScheduleParameters.createOneTime(next, 1), this);
    }
}

And schedule it for the first time with something like

Poisson poisson = RandomHelper.getPoisson();
double next = poisson.nextDouble();
RunEnvironment.getInstance().getCurrentSchedule().schedule(ScheduleParameters.createOneTime(next, 1), new ArrivalEvent(poisson));

Nick