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BIS 494: Topics in Information Systems

M/M/c Queuing Simulation with VBA (1)

Business Process Modeling, Simulation and Design

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Overview

• Problem (VBA Assignment 1)

• Logics – Flowchart– Main Sub– Arrival Sub– ServerOpen Sub– Report, and others

• Coding Flowchart

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Problem

• Spreadsheet simulation usually means creating a spreadsheet model with random numbers (e.g. exponential) in certain cell and then replicating the model with a data table and add-in such as VBA.

• Multi-server queuing system is very difficult to model with spreadsheet formulas because of the timing and bookkeeping involved (like which server has finished the service).

• A more natural approach is to take care of all the model’s logic in VBA and then simply report the results on a worksheet.

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Outline of the Simulation

• Arrival Rate (λ)

• Multiple Servers (c) with identical service rate (μ)

• Single line queue

• Limited time length (no more customers at some point of time)

• Limited queue length (?)

User Inputs

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Output

• See example Sample output.xls

• To get these values in the end, what variables should be kept for each event?

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Logic Flowchart

• Main Sub– Structure the entire logic– Subroutines are used to hide unnecessary

details– Think logics first before translating into coding

http://www.nku.edu/~sakaguch/ifs494/Main Sub Flowchart.vsd