The arrival and service distribution entries provide
the names of random variables that have been previously
defined using the Add_RV item of the Random Variables
add-in. For the example, the interarrival times
have a generalized Beta distribution ranging from
0 to 0.4. The service process is Poisson with lambda=
2 (or mean time to service of 0.5). Other simulation
parameters are: the cell location of the upper left
corner where the data and averages of the simulation
will be placed, the number of channels, the maximum
number in system if the queue is finite, random
number seeds for the arrival and service processes,
the number of arrivals to be simulated, the start
time for data collection and and the stop time for
data collection.
There are two types of simulation, Entity and
Next Event. We illustrate the entity simulation
first. A checkbox allows the student to use Exponential
distributions instead of named distributions. When
this box is checked the Arrival and Service distribution
cells accept the arrival and service rates.
There are two ways to run the simulation, dynamic
or not dynamic. The choice is determined by Dynamic
button on the dialog. A dynamic simulation places
the formulas for the simulation directly on the
worksheet. Changing the parameters of the simulation
such as number of servers, arrival rate, or random
number seeds causes the simulation to be automatically
recalculated. This provides students with immediate
feedback on the effect of queueing system design
changes. Although the number of iterations of the
simulation is not limited by the program, the dynamic
simulation requires a large amount of memory. This
may crash the system if too large a simulation is
attempted. Fifty iterations is the default value.
When the dynamic option is not selected, the formulas
are replaced by the values they produce at each
iteration. Although the results are not dynamic,
the number of iterations possible is much greater.
Entity Simulation
Pressing the OK button causes the simulation to
be performed and the results to be placed on the
worksheet. The data and results for the example
are given below.
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