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""" Market.py
Model of a supermarket.
"""
from SimPy.Simulation import *
import random
from math import sqrt
## Model components ------------------------
class Customer(Process):
def __init__(self):
Process.__init__(self)
# Randomly pick how many items this customer is buying
self.items = 1 + int(random.expovariate(1.0/AVGITEMS))
def checkout(self):
start = now() # Customer decides to check out
yield request, self, checkout_aisle
at_checkout = now() # Customer gets to front of line
waittime.tally(at_checkout-start)
yield hold, self, self.items*ITEMTIME
leaving = now() # Customer completes purchase
checkouttime.tally(leaving-at_checkout)
yield release, self, checkout_aisle
class Customer_Factory(Process):
def run(self):
while 1:
c = Customer()
activate(c, c.checkout())
arrival = random.expovariate(float(AVGCUST)/CLOSING)
yield hold, self, arrival
class Monitor2(Monitor):
def __init__(self):
Monitor.__init__(self)
self.min, self.max = (sys.maxint,0)
def tally(self, x):
self.observe(x)
self.min = min(self.min, x)
self.max = max(self.max, x)
## Experiment data -------------------------
AISLES = 6 # Number of open aisles
ITEMTIME = 0.1 # Time to ring up one item
AVGITEMS = 20 # Average number of items purchased
CLOSING = 60*12 # Minutes from store open to store close
AVGCUST = 1500 # Average number of daily customers
RUNS = 8 # Number of times to run the simulation
SEED = 111333555 # seed value for random numbers
## Model/Experiment ------------------------------
random.seed(SEED)
print 'Market'
for run in range(RUNS):
waittime = Monitor2()
checkouttime = Monitor2()
checkout_aisle = Resource(AISLES)
initialize()
cf = Customer_Factory()
activate(cf, cf.run(), 0.0)
simulate(until=CLOSING)
print "Waiting time average: %.1f" % waittime.mean(), \
"(std dev %.1f, maximum %.1f)" % (sqrt(waittime.var()),waittime.max)
## Analysis/output -------------------------
print 'AISLES:', AISLES, ' ITEM TIME:', ITEMTIME
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