Page 150 - ExtendSim User Guide
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Items, Properties, and Values
Item generation
the inputs change drastically, this can cause unexpected results as discussed in “Cycle timing” on page 312.
Generating items according to a schedule
Scheduling item arrivals can provide more flexibility and precision than having them gener- ated randomly. Setting the behavior of the Create block to “Create items by schedule” allows item arrivals to occur at fixed intervals that are specified in a table.
Scheduled Intervals model
Assume you want five items generated, one per minute, but that the simulation takes ten min- utes to run. Setting the Create block to “Create items randomly” and selecting a Constant dis- tribution would generate one item per minute, but there will be ten items. Generating items by schedule allows you to customize when items will be created and how many items the model will have.
Scheduled Intervals model
In the example model, the dialog of the Create block is set to “Create items by schedule.” The schedule of arrival times, which is cloned onto the model worksheet, indicates that one item will be generated at Create Time 1, another item at Create Time 2, and so forth up to time 5. With this schedule, the model has five arrival events.
The items proceed to a Queue to wait for processing by the Activity, which takes three minutes to process each item. Since the simulation runs for ten minutes, only three items exit; one item is left in the Queue and one item is still being processed in the Activity.
This method is especially useful when the time between item arrivals is known but not regular. For instance, the first item could be generated at Create Time 1, the second item at Create Time 3, and the third item at Create Time 3.5.
Notice that the Item Quantity column has a default value of 1 for each item generated. This means that each item generated represents 1 item. Item quantities are described fully in “Quan- tities” on page 134.
☞ An alternative method would be to use a Create block set to Create items randomly, and select a Constant distribution with a value of 1 in its dialog. Then in the block’s Options tab, select Maximum items generated: 5. This method is less flexible than the earlier method, since each item would have to have the same interval between arrivals.
The Start connector
When the Create block is set to Create items by schedule it has a start value input connector that can be used to control when the schedule is executed. The timing in the Create block depends on whether or not the start input is connected:
Discrete Event

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