Chap0019A - Chapter 19A - Simulation CHAPTER 19A SIMULATION...

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Chapter 19A - Simulation CHAPTER 19A SIMULATION Review and Discussion Questions 1. Why is simulation often called a technique of last resort? Simulation is called a technique of last resort because simulation models are time consuming to build (flow charting, coding, etc.) and do not “guarantee” an optimal solution or indeed any solution. Therefore, it makes sense to investigate other problem solving methods such as linear programming or waiting line theory before embarking on simulation. 2. What roles do statistical hypothesis testing play in simulation? A simulation can be looked upon as a test of a hypothesis. 3. What determines whether a simulation model is valid? The only true test of a simulation is how well the real system performs after the results of the simulation have been implemented. The proof of the pudding is in the eating. Prior to this stage of application, however, the simulation user can certainly evaluate the general validity of the model by comparing its results with past data or simply asking the question: “Is the information I am getting reasonable?” 4. Must you use a computer to get good information from a simulation? Explain. A computer is a must for any but the most simple simulation problems. Because simulation is a sampling process, it stands to reason that a large number of observations is desirable, and the computer is the only practical way of providing them. Of course, computerization is no guarantee of “good” information. Simulating an invalid model on the computer will only provide a larger volume of questionable data. 5. What methods are used to increment time in a simulation model? How do they work? Time incrementing methods include fixed time increments and variable time increments. With fixed time increments, uniform clock times are specified (minutes, hours, days, etc.) and the simulation proceeds by fixed intervals from one time period to the next. At each point in clock time, the system is scanned to determine if any events have occurred and time is advanced; if none have, time is still advanced by one unit. With variable time increments, the clock time is advanced by the amount required to initiate the next event. It is interesting to note that variable time incrementing generally is more difficult to program unless one is using a special simulation language such as GPSS. 23
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Chapter 19A - Simulation 6. What are the pros and cons of starting a simulation with the system empty? With the system in equilibrium? The pros of starting a simulation with the system empty are that this enables evaluation of the transient period in terms of time to reach steady-state and the activities which are peculiar to the transient period. One con is that it takes a longer period of time to perform the simulation.
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Chap0019A - Chapter 19A - Simulation CHAPTER 19A SIMULATION...

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