#You define the Level resource facility lev by a statement like this:
#lev = Level(name='a_level', unitName='units', # capacity='unbounded', initialBuffered=0, # putQType=FIFO, getQType=FIFO, # monitored=False, monitorType=Monitor)
#Example. Suppose that a random demand on an inventory is made each day. Each requested amount is distributed normally with a #mean of 1.2 units and a standard deviation of 0.2 units. The inventory (modeled as an object of the Level class) is refilled by #10 units at fixed intervals of 10 days. There are no back-orders, but a accumulated sum of the total stock-out quantities is to #be maintained. A trace is to be printed out each day and whenever there is a stock-out:
from SimPy.Simulation import * from random import normalvariate,seed class Deliver(Process): def deliver(self): # an "offeror" PEM while True: lead = 10.0 # time between refills delivery = 10.0 # amount in each refill yield put, self, stock, delivery print 'at %7.4f, add %7.4f units, now amount = %6.4f'\ %(now(),delivery,stock.amount) yield hold, self, lead class Demand(Process): stockout = 0.0 # initialize initial stockout amount def demand(self): # a "requester" PEM day = 1.0 # set time-step to one day while True: yield hold, self, day dd = normalvariate(1.20, 0.20) # today's random demand ds = dd - stock.amount # excess of demand over current stock amount if dd > stock.amount: # can't supply requested amount yield get, self, stock, stock.amount # supply all available amount self.stockout += ds # add unsupplied demand to self.stockout print 'day %7.4f, demand = %7.4f, \ shortfall = %7.4f' %(now(), dd, -ds) else: # can supply requested amount yield get, self, stock, dd print 'day %7.4f, supplied %7.4f, now amount = %6.4f'\ %(now(), dd, stock.amount)stock = Level(monitored=True) # 'unbounded' capacity and other defaults seed(99999) initialize() offeror = Deliver()activate (offeror, offeror.deliver())requester = Demand()activate (requester, requester.demand()) simulate (until=49.9) result=(stock.bufferMon.mean(), requester.stockout) print print 'Summary of results through end of day %7.4f:' %(int(now())) print 'average stock = %7.4f, cumulative stockout = %7.4f' %result
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at 0.0000, add 10.0000 units, now amount = 10.0000
day 1.0000, supplied 1.0115, now amount = 8.9885
day 2.0000, supplied 1.1377, now amount = 7.8508
day 3.0000, supplied 0.7743, now amount = 7.0766
day 4.0000, supplied 1.4056, now amount = 5.6709
day 5.0000, supplied 0.9736, now amount = 4.6973
day 6.0000, supplied 1.1061, now amount = 3.5912
day 7.0000, supplied 1.4067, now amount = 2.1845
day 8.0000, supplied 1.2884, now amount = 0.8961
day 9.0000, demand = 1.4426, shortfall = -0.5465
at 10.0000, add 10.0000 units, now amount = 10.0000
day 10.0000, supplied 1.5850, now amount = 8.4150
day 11.0000, supplied 0.7974, now amount = 7.6176
day 12.0000, supplied 0.8854, now amount = 6.7323
day 13.0000, supplied 1.4893, now amount = 5.2430
day 14.0000, supplied 1.0522, now amount = 4.1908
day 15.0000, supplied 1.0492, now amount = 3.1416
day 16.0000, supplied 1.2013, now amount = 1.9403
day 17.0000, supplied 1.4026, now amount = 0.5377
day 18.0000, demand = 1.0874, shortfall = -0.5497
day 19.0000, demand = 1.3043, shortfall = -1.3043
at 20.0000, add 10.0000 units, now amount = 10.0000
day 20.0000, supplied 1.2737, now amount = 8.7263
day 21.0000, supplied 0.9550, now amount = 7.7713
day 22.0000, supplied 1.3646, now amount = 6.4067
day 23.0000, supplied 0.8629, now amount = 5.5438
day 24.0000, supplied 1.2893, now amount = 4.2545
day 25.0000, supplied 1.1897, now amount = 3.0648
day 26.0000, supplied 0.9708, now amount = 2.0940
day 27.0000, supplied 1.1397, now amount = 0.9543
day 28.0000, demand = 1.1286, shortfall = -0.1743
day 29.0000, demand = 0.8891, shortfall = -0.8891
at 30.0000, add 10.0000 units, now amount = 10.0000
day 30.0000, supplied 0.9496, now amount = 9.0504
day 31.0000, supplied 1.1515, now amount = 7.8988
day 32.0000, supplied 1.3724, now amount = 6.5264
day 33.0000, supplied 0.6977, now amount = 5.8287
day 34.0000, supplied 1.2291, now amount = 4.5996
day 35.0000, supplied 1.3502, now amount = 3.2494
day 36.0000, supplied 1.0396, now amount = 2.2098
day 37.0000, supplied 1.3442, now amount = 0.8656
day 38.0000, demand = 1.0919, shortfall = -0.2263
day 39.0000, demand = 1.4077, shortfall = -1.4077
at 40.0000, add 10.0000 units, now amount = 10.0000
day 40.0000, supplied 0.9053, now amount = 9.0947
day 41.0000, supplied 1.2982, now amount = 7.7965
day 42.0000, supplied 1.3458, now amount = 6.4508
day 43.0000, supplied 1.2357, now amount = 5.2151
day 44.0000, supplied 1.2822, now amount = 3.9329
day 45.0000, supplied 1.1809, now amount = 2.7519
day 46.0000, supplied 1.0891, now amount = 1.6629
day 47.0000, supplied 1.1926, now amount = 0.4702
day 48.0000, demand = 1.3927, shortfall = -0.9224
day 49.0000, demand = 1.2690, shortfall = -1.2690
Summary of results through end of day 49.0000:
average stock = 4.4581, cumulative stockout = 7.2894