Why is this recursive statement wrong?
This is a banking simulation that accounts for 20 different service lines in one queue, customers arrive at an exponential rate and are served over a time that follows a normal distribution with a mean of 40 and a standard deviation of 20.
Everything worked fine until I decided to exclude the negative values given by the normal distribution using this method:
def getNormal(self):
normal = normalvariate(40,20)
if (normal>=1):
return normal
else:
getNormal(self)
Am I messing up the recursive call? I don't understand why this won't work. I changed the getNormal () method to:
def getNormal(self):
normal = normalvariate(40,20)
while (normal <=1):
normal = normalvariate (40,20)
return normal
But I'm curious as to why the previous recursive statement went bankrupt.
This is the complete source code if you're interested.
""" bank21: One counter with impatient customers """
from SimPy.SimulationTrace import *
from random import *
## Model components ------------------------
class Source(Process):
""" Source generates customers randomly """
def generate(self,number):
for i in range(number):
c = Customer(name = "Customer%02d"%(i,))
activate(c,c.visit(tiempoDeUso=15.0))
validateTime=now()
if validateTime<=600:
interval = getLambda(self)
t = expovariate(interval)
yield hold,self,t #esta es la rata de generación
else:
detenerGeneracion=999
yield hold,self,detenerGeneracion
class Customer(Process):
""" Customer arrives, is served and leaves """
def visit(self,tiempoDeUso=0):
arrive = now() # arrival time
print "%8.3f %s: Here I am "%(now(),self.name)
yield (request,self,counter),(hold,self,maxWaitTime)
wait = now()-arrive # waiting time
if self.acquired(counter):
print "%8.3f %s: Waited %6.3f"%(now(),self.name,wait)
tiempoDeUso=getNormal(self)
yield hold,self,tiempoDeUso
yield release,self,counter
print "%8.3f %s: Completed"%(now(),self.name)
else:
print "%8.3f %s: Waited %6.3f. I am off"%(now(),self.name,wait)
## Experiment data -------------------------
maxTime = 60*10.5 # minutes
maxWaitTime = 12.0 # minutes. maximum time to wait
## Model ----------------------------------
def model():
global counter
#seed(98989)
counter = Resource(name="Las maquinas",capacity=20)
initialize()
source = Source('Source')
firstArrival= expovariate(20.0/60.0) #chequear el expovariate
activate(source,
source.generate(number=99999),at=firstArrival)
simulate(until=maxTime)
def getNormal(self):
normal = normalvariate(40,20)
if (normal>=1):
return normal
else:
getNormal(self)
def getLambda (self):
actualTime=now()
if (actualTime <=60):
return 20.0/60.0
if (actualTime>60)and (actualTime<=120):
return 25.0/60.0
if (actualTime>120)and (actualTime<=180):
return 40.0/60.0
if (actualTime>180)and (actualTime<=240):
return 30.0/60.0
if (actualTime>240)and (actualTime<=300):
return 35.0/60.0
if (actualTime>300)and (actualTime<=360):
return 42.0/60.0
if (actualTime>360)and (actualTime<=420):
return 50.0/60.0
if (actualTime>420)and (actualTime<=480):
return 55.0/60.0
if (actualTime>480)and (actualTime<=540):
return 45.0/60.0
if (actualTime>540)and (actualTime<=600):
return 10.0/60.0
## Experiment ----------------------------------
model()
source to share
I think what you want
return getnormal(self)
instead
getnormal(self)
If the function exits without hitting a return statement, then the special value None is returned, which is a NoneType object, which is why Python complains about "NoneType". The abs () function wants a number and it doesn't know what to do with None.
Alternatively, you can avoid recursion (and the cost of creating a new stack frame) with
def getNormal(self):
normal = 0
while normal < 1:
normal = normalvariate(40,20)
return normal
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