CSci 405: Computer Simulation
Spring Semester 2000

Assignment #2
Due Wednesday, 29 March, 11:00 A.M. (Revised)

Prepare this assignment by the above deadline in accordance with the instructions given in the Professional Conduct and Assignments sections of the Syllabus .

You may work individually or in groups of two persons. (Both individuals in a group should be familiar with all aspects of the model and implementation code and be able to explain it to the instructor.)

In this assignment you are asked to develop a simulation model and program using Java and the JavaSim simulation package. The JavaSim package is available on the course's Web pages, is installed on system john, and will be made available on the Adler lab systems soon.

Develop a simulation model of a facility such as the Adler computer laboratory in the department. The facility has the following characteristics:

• There are nComp identically configured personal computers that can be used by students on a first-come-first-served basis.
• The students arrive to use the lab at time intervals that can be modeled by an exponential distribution with mean of arrMean minutes.
• Students use computers for periods of time that can be modeled with an exponential distribution with a mean of useMean minutes.
• If all computers are occupied, students will wait for a free one with a probability of waitProb. The remaining students will leave and try again later. The waiting queue is FIFO and unbounded in length.
• Students will be open for openPeriod minutes. After openPeriod minutes no more students will be admitted, but those already in the lab will be allowed to finish their use period.

Do the following experiments, letting arrMean = 10 minutes, useMean = 90 minutes, waitProb be two-thirds, and openPeriod = 16 hours in your model,

1. Assume that nComp is unbounded. How many students arrived? How many were served? What is the average number of computers needed in the lab? What is the maximum number of computers needed in the lab at any one time during the simulation? (You may want to instrument your program to collect other useful information.)
2. Repeat the experiment in (1), except set nComp to the average number of computers in use during the simulation (rounded up to the nearest integer). Now, what percentage of students cannot get access to a computer on their first try without waiting? What percentage of the students leave without getting use of a computer on their first try?
3. Repeat the experiment in (1), but this time increase nComp by one from what you used in (2). Answer the same questions as in (2).
4. Repeat the experiment in (a), but this time increase nComp by two from what you used in (2). Answer the same questions as in (2)

Interesting enhancements:

• Allow the arrival rates, usage period means to change depending upon period of time during the day, day of the week, nearness of an assignment deadline, etc.
• Use real data from use of the Adler lab to determine appropriate distributions and/or to enable a usage trace to drive the simulation.
• Model disruptions in usage such as the use of the lab to hold a class.
• Model failure and repair periods for computers and the corresponding disruptions in usage.

When this assignment is complete, submit:

• a description of your model in text and drawings,
• a paper listing of your program source code and outputs from your experiments,
• clearly marked answers to the question above,
• a diskette containing your program source code.

Be sure that all items submitted are clearly labeled with your name, class, and the assignment number.

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