| SAS/OR: The QSIM Application |
Random and Exogenous Variation in the Model
Random and exogenous sources of variation play a central
role in discrete event simulation.
The
Sampler,
Server, MServer,
and formulas are the principle sources of this variation
in the QSIM models.
However, there are other situations where variation
can be meaningfully incorporated into models.
For example, you may want to delay the
effect of a Trigger
for some random or fixed
amount of time.
In each of these cases
you have access to a combo box, such as the one in the
Sampler
control panel shown in Figure 6.1,
labeled to show the use of the source of variation.
In this case, it is the time between transaction arrivals to
the system.
If you click on the down arrow, a list that includes
the possible distributions is displayed.
Figure 6.1: Sources of Variation
When you select one of these distributions,
the selection is displayed in the text area to
the left of the down arrow.
For each distribution you select, you can set one or more parameters
which further define the choice.
There are two types of sources of variation: random and
exogenous.
These are not mutually exclusive.
That is, an exogenous source of variation can be randomly
generated.
