Simulation-with-Arena仿真与竞技场课件

1、Chapter 1What is Simulation?Chapter 1What is Simulation?Simulation Is .Very broad term, set of problems/approachesGenerally, imitation of a system via computerInvolves a model validity?Dont even aspire to analytic solutionDont get exact results (bad)Allows for complex, realistic models (good)Approxi

2、mate answer to exact problem is better than exact answer to approximate problemConsistently ranked as most useful, powerful of mathematical-modeling approaches2Simulation with Arena Chapter 1 What is Simulation?Simulation Is .Very broad teSome Application AreasManufacturing scheduling, inventoryStaf

3、fing personal-service operationsBanks, fast food, theme parks, Post Office, .Distribution and logisticsHealth care emergency, operating roomsComputer systemsTelecommunicationsMilitaryPublic policyEmergency planningCourts, prisons, probation/parole3Simulation with Arena Chapter 1 What is Simulation?S

4、ome Application AreasManufactSystemsPhysical facility/process, actual or plannedStudy its performanceMeasureImproveDesign (if it doesnt exist)Maybe control in real timeSometimes possible to “play” with the systemBut sometimes impossible to do soDoesnt existDisruptive, expensive4Simulation with Arena

5、 Chapter 1 What is Simulation?SystemsPhysical facility/proceModelsAbstraction/simplification of the system used as a proxy for the system itselfCan try wide-ranging ideas in the modelMake your mistakes on the computer where they dont count, rather for real where they do countIssue of model validityT

6、wo types of modelsPhysical (iconic)Logical/Mathematical quantitative and logical assumptions, approximations5Simulation with Arena Chapter 1 What is Simulation?ModelsAbstraction/simplificatiWhat Do You Do with a Logical Model?If model is simple enough, use traditional mathematics (queueing theory, d

7、ifferential equations, linear programming) to get “answers”Nice in the sense that you get “exact” answers to the modelBut might involve many simplifying assumptions to make the model analytically tractable validity?Many complex systems require complex models for validity simulation needed6Simulation

8、 with Arena Chapter 1 What is Simulation?What Do You Do with a Logical Computer SimulationMethods for studying a wide variety of models of real-world systemsUse numerical evaluation on computerUse software to imitate the systems operations and characteristics, often over timeIn practice, is the proc

9、ess of designing and creating computerized model of system and doing numerical computer-based experimentsReal power application to complex systemsSimulation can tolerate complex models7Simulation with Arena Chapter 1 What is Simulation?Computer SimulationMethods forPopularityM.S. grads, CWRU O.R. De

10、partment (1978)Asked about value after graduation; rankings:1. Statistical analysis, 2. Forecasting, 3. Systems analysis, 4. Information systems5. Simulation137 large firms (1979)1. Statistical analysis (93% used it)2. Simulation (84%)Followed by LP, PERT/CPM, inventory, NLP8Simulation with Arena Ch

11、apter 1 What is Simulation?PopularityM.S. grads, CWRU O.RPopularity (contd.)(A)IIE, O.R. division members (1980)First in utility and interest: SimulationBut first in familiarity: LP (simulation was second)Longitudinal study of corporate practice (1983, 1989, 1993)1. Statistical analysis2. Simulation

12、Survey of such surveys (1989)Consistent heavy use of simulation9Simulation with Arena Chapter 1 What is Simulation?Popularity (contd.)(A)IIE, O.Advantages of SimulationFlexibility to model things as they are (even if messy and complicated)Avoid “looking where the light is” (a morality play):Allows u

13、ncertainty, nonstationarity in modelingThe only thing thats for sure: nothing is for sureDanger of ignoring system variabilityModel validityYoure walking along in the dark and see someone on hands and knees searching the ground under a street light.You:“Whats wrong? Can I help you?”Other person:“I d

14、ropped my car keys and cant find them.”You:“Oh, so you dropped them around here, huh?”Other person:“No, I dropped them over there.” (Points into the darkness.)You:“Then why are you looking here?”Other person:“Because this is where the light is.”10Simulation with Arena Chapter 1 What is Simulation?Ad

15、vantages of SimulationFlexibAdvantages of Simulation (contd.)Advances in computing/cost ratiosEstimated that 75% of computing power is used for various kinds of simulationsDedicated machines (e.g., real-time shop-floor control)Advances in simulation softwareFar easier to use (GUIs)No longer as restr

16、ictive in modeling constructs (hierarchical, down to C)Statistical design & analysis capabilities11Simulation with Arena Chapter 1 What is Simulation?Advantages of Simulation (contThe Bad NewsDont get exact answers, only approximations, estimatesAlso true of many other modern methodsCan bound errors

17、 by machine roundoffGet random output (RIRO) from stochastic simulationsStatistical design, analysis of simulation experimentsExploit: noise control, replicability, sequential sampling, variance-reduction techniquesCatch: “standard” statistical methods seldom work 12Simulation with Arena Chapter 1 W

18、hat is Simulation?The Bad NewsDont get exact anDifferent Kinds of SimulationStatic vs. DynamicDoes time have a role in the model?Continuous-change vs. Discrete-changeCan the “state” change continuously or only at discrete points in time?Deterministic vs. StochasticIs everything for sure or is there

19、uncertainty?Most operational models:Dynamic, Discrete-change, Stochastic13Simulation with Arena Chapter 1 What is Simulation?Different Kinds of SimulationSEstimate p (George Louis Leclerc, c. 1733)Toss needle of length l onto table with stripes d (l) apartP (needle crosses a line) =Repeat; tally = p

20、roportion of times a line is crossedEstimate p bySimulation by Hand:The Buffon Needle Problem14Simulation with Arena Chapter 1 What is Simulation?Simulation by Hand:The BuffonWhy Toss Needles?Buffon needle problem seems silly now, but it has important simulation features:Experiment to estimate somet

21、hing hard to compute exactly (in 1733)Randomness, so estimate will not be exact; estimate the error in the estimateReplication (the more the better) to reduce errorSequential sampling to control error keep tossing until probable error in estimate is “small enough”Variance reduction (Buffon Cross)15S

22、imulation with Arena Chapter 1 What is Simulation?Why Toss Needles?Buffon needleUsing Computers to SimulateGeneral-purpose languages (FORTRAN)Tedious, low-level, error-proneBut, almost complete flexibilitySupport packagesSubroutines for list processing, bookkeeping, time advanceWidely distributed, w

23、idely modifiedSpreadsheetsUsually static modelsFinancial scenarios, distribution sampling, SQC16Simulation with Arena Chapter 1 What is Simulation?Using Computers to SimulateGenUsing Computers to Simulate (contd.)Simulation languagesGPSS, SIMSCRIPT, SLAM, SIMANPopular, in wide use todayLearning curv

24、e for features, effective use, syntaxHigh-level simulatorsVery easy, graphical interfaceDomain-restricted (manufacturing, communications)Limited flexibility model validity?17Simulation with Arena Chapter 1 What is Simulation?Using Computers to Simulate (cWhere Arena Fits InHierarchical structureMult

25、iple levels of modelingCan mix different modeling levels together in the same modelOften, start high then go lower as neededGet ease-of-use advantage of simulators without sacrificing modeling flexibilityArena TemplateStandard EditionProfessional EditionA singlegraphical userinterfaceconsistent atan

26、y level ofmodelingHigherLevel ofModelingLowerSIMAN TemplateVertical SolutionsUser-Created Templates Commonly used constructs Company-specific processes Company-specific templates etc.Application Solution Templates Call$im BP$im etc.Common Panel Many common modeling constructs Very accessible, easy t

27、o use Reasonable flexibilitySupport, Transfer Panels Access to more detailed modeling for greater flexibilityBlocks, Elements Panels All the flexibility of the SIMAN simulation languageUser-Written Visual Basic, C/C+, FORTRANCode The ultimate in flexibility C/C+/FORTRAN requires compiler18Simulation

28、 with Arena Chapter 1 What is Simulation?Where Arena Fits InHierarchicaWhen Simulations are UsedUses of simulation have evolved with hardware, softwareThe early years (1950s-1960s)Very expensive, specialized tool to useRequired big computers, special trainingMostly in FORTRAN (or even Assembler)Proc

29、essing cost as high as $1000/hour for a sub-286 level machine19Simulation with Arena Chapter 1 What is Simulation?When Simulations are UsedUses When Simulations are Used (contd.)The formative years (1970s-early 1980s)Computers got faster, cheaperValue of simulation more widely recognizedSimulation software improved, but they were still languages to be learned, typed, batch processedOften used to clean up “disasters” in auto, aerospace indus