General Steps in Computer Modeling

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General Steps in Computer Modeling
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Formulate the problem and plan the study

• problem of interest is stated by manager
• one or more kickoff meetings for the study are
  conducted, with the project manager, the
  simulation analysts, and subject-matter experts
  in attendance.
• issues discussed
• overall objectives of the study
• specific questions to be answered by the study
• performance measures that will be used to
  evaluate the efficacy of different system
  configurations

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Formulate the problem and plan the study

• issues discussed (cont)
• scope of the model
• system configurations to be modeled
• software to be used
• time frame for the study and the required
  resources

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Collect data and define a model

• collect information on the system layout and
  operating procedures
• no single person or document is sufficient
• some people may have inaccurate information
  make sure that true SMEs are identified
• operating procedures may not be formalized
• collect data (if possible) to specify model
  parameters and input probability distributions

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Collect data and define a model

• delineate the above information and data in an
  assumptions document, which is the conceptual
  model
• collect data on the performance of the existing
  system (for validation purposes)
• there need not be a one-to-one correspondence
  between each element of the model and the
  corresponding element of the system
• interact with the manager on a regular basis

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Collect data and define a model

• the level of model detail should depend on the
  following
• project objectives
• performance measures
• data availability
• credibility concerns
• computer constraints
• opinions of SMEs
• time and money constraints

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Is the conceptual model valid?

• perform a structured walk-through of the
  conceptual model using the assumptions document
  before an audience of managers, analysts, and
  SMEs
• help ensure that the models assumptions are
  correct and complete
• promotes ownership of the model
• takes place before programming begins to avoid
  significant reprogramming later

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Construct a computer program and verify

• program the model in a programming language or
  in simulation software
• verify (debug) the simulation computer program

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Is the programmed model valid?

• if there is an existing system, then compare
  model and system performance measures for the
  existing system
• regardless of whether there is an existing
  system, the simulation analysts and SMEs should
  review the model results for correctness
• use sensitivity analyses to determine what model
  factors have a significant impact on performance
  measures and, thus, have to be modeled correctly

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Design experiments

• specify the following for each system
  configuration of interest
• length of each run
• length of the warmup period, if one is
  appropriate
• number of independent simulation runs using
  different random numbers

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Make production runs

• production runs are made to be used in the next
  step

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Analyze output data

• two major objectives in analyzing output data
  are
• determining the absolute performance of certain
  system configurations
• comparing alternative system configurations in a
  relative sense

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Document, present, and use results

• document assumptions, computer program, and
  studys results for use in the current and future
  projects
• present studys result
• use animation to communicate model to managers
  and other people who are not familiar with all of
  the model details
• discuss model building and validation process to
  promote credibility

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Document, present, and use results

• results are used in decision-making process if
  they are both valid and credible.