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The simulation process
Like all tasks, you can start modeling simply by jumping into it. Also like other tasks, it is usu- ally better to have a plan before starting. ExtendSim makes following a plan for making a model easy. The basic steps to creating a model are:
1) Formulatetheproblem.Youshoulddefinetheproblemandstatetheobjectivesofthe model.
2) Describetheflowofinformation.Determinewhereinformationflowsfromonepartof the model to the next and which parts need information simultaneously.
3) Buildandtestthemodel.BuildthesystemwithExtendSim’sblocks.Startsmall,testas you build, and enhance as needed.
4) Acquiredata.Identify,specify,andcollectthedatayouneedforthemodel.Thisisusually the most time-consuming step. It includes finding not only numerical data values but also mathematical formulas such as distributions for random events.
5) Runthemodel.Determinehowlongyouwanttosimulateandthegranularityofresults, then run your model.
6) Verifythesimulationresults.Comparethemodelresultstowhatyouintendedor expected.
7) Validatethemodel.Comparethemodeltotherealsystem,ifavailable.Orhavesystem experts evaluate the model and its results.
8) Analyzeyourresults.Drawinferencesfromthemodel’sresultsandmakerecommenda- tions on how the system can change.
9) Conductexperiments.Implementandtestrecommendedchangesinthemodel.
10)Document. State the model’s purpose, assumptions, techniques, modeling approaches,
data requirements, and results.
11) Implement your decisions. Use the results in the real world.
Before you build a model
Remember that building a model is an iterative process and each step in the process will require comparing the model to the existing system, analyzing the results, and refining the model. A natural inclination is to immediately start building the model. However, you will end up with more useful models if you begin the model-building process by asking a few basic questions, such as:
• Whatisthegoalofthemodel?Itisimportanttodeterminethepurposeofamodel.Thiswill indicate the levels of detail required and will help keep you focused.
• Whataretheboundariesofthemodelandwhatlevelofdetailshouldbeincluded?The model goal should dictate what to include in the model and what to leave out.
Simulation Concepts 57
The modeling process

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