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652 Analysis
Scenario analysis
Tutorial I (dialog parameters)
☞ Most analysts would only use dialog parameters in their scenarios, so this tutorial focuses on those. For advanced analysis, you can also use databases, tables, and so forth, as discussed on page 658.
The following example uses the Final Car Wash model from the User Guide’s Discrete Event tutorial to investigate how changes in a number of factors affect the average wait time and throughput.
The table below shows the model factors and how they will be varied:
Number of attendants Wash only time Wash and wax time Car interarrival rate
1, 2, 3
5, 6, 7
6, 7, 8
3, 3.5, 4, 4.5, 5
Each scenario will be run 5 times to capture the variation in the results between one run and the next. To evaluate all of the possible combinations requires 675 replications (135 scenarios ((3 x 3 x 3 x 5 levels)) at 5 runs each).
☞ Fortunately, this model runs very quickly so this number of replications is not a problem. How- ever, if the model took significantly longer to run or if there were more factors, a design of experiments (DOE) should be used to reduce the number of scenarios.
The steps for performing scenario analysis are:
1) AddaScenarioManagerblock(Valuelibrary,ExtendSimATandExtendSimSuiteonly)to a model
2) Identifyandaddthefactors(modelinputs)youwantincludedintheanalysis
3) Identifyandaddtheresponses(modelresults)youwanttoanalyze
4) Determinewhatyouwantinthereport
5) DeterminetheDOE,thengenerateandrunthescenarios
6) Analyzetheresults
7) Optional.ExportthescenariostoExcel,JMP,Minitab,atextfile,oranExtendSimdata- base for further analysis
Add the Scenario Manager block
Open the model named Final Car Wash (\Examples\Tutorials\Discrete Event)
Save the model as “Final Car Wash Scenarios” so you don’t overwrite the original model
Place a Scenario Manager block (Value library, ExtendSim AT and ExtendSim Suite only) in the model. The block can be placed anywhere but the top of the model will provide easi- est access.
Since all the other blocks are labeled, label the block “Scenario Manager”
How To

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