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Cork Institute of Technology
Master of Science in Software Development - Award
(NFQ – Level 9)
Summer 2007
Computer Simulation & Modelling
(Time: 2 Hours)
Instructions Answer any THREE questions. Note: Question 1 = 34 marks All other questions = 33 marks
Examiners: Dr. John Creagh Dr. Bing Wu Dr. James Power
Q1. (a) (i) Briefly define the four main approaches to “Input to Simulation”. (4 marks) (ii) Define the three basic types of parameters for parameterising probability density functions. Clear diagrams required. (6 marks) (iii) From a modelling viewpoint, explain the usefulness of each of the following distributions:
- Triangular
- Weibull
- Exponential (6 marks) (iv) How may you estimate the values of the parameters of the following distributions:
- Normal
- Exponential
- Lognormal
- Gamma (5 marks)
(b) When analysing observed data, explain the approach necessary for using theoretical distribution when outliners and multiple peaks are found. Example required. (6 marks)
(c) Referring to the four main approaches to “Input to Simulation”, what advice would you give a modeller for choosing an approach? Clearly list your points, justify each point you make. Examples required. (7 marks)
Q2. (a) A network device has ports for processing incoming data. This problem focuses on a single port. Data arrives at the port data unit by data unit. The average data unit size is 10 packets. The size of a packet is 1 KB. A single port must process an average 36000 packets per hour. Assume exponential arrival rate. The port capacity is 7200 data units per minute. Assume exponential service rate. Develop a queuing system to answer the following question: What memory size would you recommend from the following list of options, 60K, 120K, 180K or 240K? Explain and justify your answer. (17 marks)
(b) (i) “Pseudo-random number generation acts as a cornerstone of discrete-event simulation”. Justify this statement. Clear examples required. (7 marks) (ii) Write an algorithm and give the C/C++ code structure for the generation of exponential continuous random variates. An explanation is required. (9 marks)
Q3. (a) The Arena simulation package uses flow-charting based modelling. (i) Give an overview description of Arena flow-charting. Focus on the most commonly used blocks in the basic process panel. (6 marks) (ii) Give examples of Arrival, Process, Decide and Dispose Arena blocks. Show the corresponding relationship with the SIMAN language. Explanation required. (8 marks)
(b) Utilising the Law and Kelton simlib library, give the outline code structure/algorithms for the development of a discrete event simulation program for a M/M/3 queuing system, exponential service rate mean of 20, and exponential service rate mean of 25. Comments and descriptions are required. (14 marks)
(c) Critics of spreadsheet simulation specify many disadvantages. Firstly, list and explain the main disadvantages. Then, give reasons why you think spreadsheet simulation is gaining popularity. Justify. (5 marks)
