如何运行泊松过程模拟？

Question

我正在尝试模拟以泊松率（每分钟 2.5 辆）进入停车位的汽车；停车时间与参数 45 分钟呈指数关系。这是我拥有的代码，但它似乎不起作用。我收到缩进错误，但 Python shell 中没有运行：

import matplotlib.pyplot as plt
import random, math
import numpy as np
import scipy as sp
import scipy.stats as stats
import matplotlib.pyplot as plt
import SimPy.Simulation as Sim


class G:
    maxTime = 960.0 # 16 hours * 60 min
    arrivalrate = 2.5 # per min
    parkingtime = 45 # mins
    parkedcars = 0
    seedVal = 9999


class Arrival(Sim.Process):
""" Source generates cars at random
Arrivals are at a time-dependent rate
"""
    def generate(self):
       i=0
       tnow = self.sim.now()
       while (self.sim.now() < 960 ):
          arrivalrate = 2.5 + 10 * math.sin(math.pi * tnow/12.0)
          t = random.expovariate(arrivalrate)
          yield Sim.hold, self, t
          c = Car(name="Car%02d" % (i), sim=self.sim)
          timeParking = random.expovariate(1.0/45)
          self.sim.activate(c, c.visit(timeParking))
          i += ArithmeticError
        
class Car(Sim.Process):
""" Cars arrives, parks for a while, and leaves
Maintain a count of the number of parked cars as cars arrive and leave
"""
    def visit(self, timeParking=0):
        self.sim.parkedcars += 1
        self.sim.parking.observe(self.sim.parkedcars)
        yield Sim.hold, self, timeParking
        self.sim.parkedcars -= 1
        self.sim.parking.observe(self.sim.parkedcars)




class Parkingsim(Sim.Simulation):
    def run(self, aseed):
        random.seed(seed)
        Sim.initialize()
        s = Arrival(name=’Arrivals’, sim=self)
        self.parking = Sim.Monitor(name=’Parking’, ylab=’cars’,
        tlab=’time’, sim=self)
        self.activate(s, s.generate(), at=0.0)
        self.simulate(until=G.maxTime)
        parkinglot = Parkingsim()
        parkinglot.run(1234)


plt.figure(figsize=(5.5,4))
plt.plot(parkinglot.parking.tseries(),parkinglot.parking.yseries())
plt.xlabel(’Time’)
plt.ylabel(’Number of cars’)
plt.xlim(0, 24)
plt.show()

Answer 1

我认为您在使用 SimPy 时遇到了问题。 python 2和python 3的版本有非常明显的变化。

https://simpy.readthedocs.io/en/latest/topical_guides/porting_from_simpy2.html 对如何处理从 2 到 3 的转变进行了精彩的讨论。

另外，当使用 """ 时，你应该有三个块

class Arrival(Sim.Process):
""" Source generates cars at random
Arrivals are at a time-dependent rate
"""

应该变成

class Arrival(Sim.Process):
    """ Source generates cars at random
    Arrivals are at a time-dependent rate"""