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``````122 Items, Properties, and Values
Item generation
Choosing a distribution in the Create block
The dialog of the Create block con- tains several distribution choices in its “Specify a distribution” popup menu, as well as a table for entering data when an empirical distribution is selected. Each distribution is described in the Create block’s Help; they are also discussed briefly in “Probability distributions” on
page 704.
Choosing a distribution in the dialog of the Create block defines both the interval between item arrivals (the interarrival time) and the characteris- tics of the rate of arrival.
Exponential distribution selected; mean is 4
In the Car Wash model, for example, selecting an exponential distribution with a mean of 4 will cause one car to arrive approximately every 4 minutes for the duration of the simulation. This results in an interarrival time of 4. However, the shape of the exponential distribution dic- tates that it is more likely that the time between arrivals will be between 0 and 4 than between 4 and 8.
Distribution of outputs when mean is 4
Random intervals with dynamic
parameters
You may want the parameters in a random distribution to change as a function of time or model status during the simulation run. The arguments for a given distribution can be controlled dynamically through the Create block's value input connectors.
Random Intervals model
In the Random Intervals model, time dependent arrival rates are modeled by connecting the Lookup Table block (Value library) to the Create block’s value input connectors. A table in the Lookup Table block provides the mean values for an exponential distribution that has been set in the Create block. This causes the timing of item arrivals to be based on the time of day.
Random Intervals model
Discrete Event

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