singleserverqueue.py

import random

if __name__ == "__main__":
    #  define and initialize queue variables
    lambd_in = 0.5
    lambd_out = 0.4
    closing_time = 100
    t = 0
    num_arrivals = 0
    num_departures = 0
    n = 0
    time_depart = float('inf')
    time_arrive = random.expovariate(lambd_in)
    departures = []
    arrivals = []
    overtime = 0
    max_line_length = 0
    while t < closing_time or n > 0:
        # case 1 - arrival before next departure
        if time_arrive <= time_depart and time_arrive <= closing_time:
            t = time_arrive      # move along to time ta
            num_arrivals += 1     # one additional arrival
            n += 1      # one additional customer
            # generate time of next arrival
            time_arrive = random.expovariate(lambd_in) + t
            # generate time of departure if queue has been empty
            if n == 1:
                Y = random.expovariate(lambd_out)
                time_depart = t + Y
            arrivals.append(t)
            print("Arrival ", num_arrivals, "at time ", t)

        # case 2 - departure before next arrival
        elif time_depart < time_arrive and time_depart <= closing_time:
            # advance time to next departure
            t = time_depart
            # one less person in line
            n -= 1
            # one more person served
            num_departures += 1
            # if queue is empty, infinite time of next departure
            if n == 0:
                time_depart = float('inf')
            # if queue isn't empty, generate next time of departure
            else:
                Y = random.expovariate(lambd_out)
                time_depart = t + Y
            departures.append(t)
            print("Departure ", num_departures, "at time ", t)

        # case 3 - next arrival/departure happens after closing time and there are people still in queue
        elif min(time_arrive, time_depart) > closing_time and n > 0:
            # advance time to next departure
            t = time_depart
            # one less person in line
            n -= 1
            # one more person served
            num_departures += 1
            # if line isn't empty, generate time of next departure
            if n > 0:
                Y = random.expovariate(lambd_out)
                time_depart = t + Y
            departures.append(t)
            # print("Departure ", nd, "at time ", t)

        # case 4 - next arrival/departure happens after closing time and there is nobody left in the queue
        elif min(time_arrive, time_depart) > closing_time and n == 0:
            # calculate overtime
            overtime = max(t-closing_time, 0)
            break

    print("Overtime: ", overtime)