Page 161 - ExtendSim User Guide
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Items, Properties, and Values 135
Item properties
For most purposes you would not want to change the quantity of an item from its default value of 1. However, to model a change of shift consisting of five workers going off duty at the same time, to simulate the delivery of a box of 300 pieces of mail to a mail room, or for similar situ- ations, set the quantity of the item to be other than 1.
How blocks treat items with quantities other than 1
Items with quantities other then 1 are treated differently depending on the nature of the block processing them. They will travel together as a unit, being processed essentially as one item, until they reach an Exit, a Queue, a Batch, or a Resource Item block, or are sent into a univer- sal connector (such as Change, Demand, Select, or Start.)
• When an item with a quantity other then 1 reaches an Exit, Queue, Batch, or Resource Item block, it is decomposed into separate identical items. For example, when it enters a Queue, an item with a quantity of 10 will become 10 distinct items, each with a quantity of 1 and each with the same properties (attributes, priority, and so on) of the original item. An item with a quantity of 0 will disappear when it reaches a Queue.
• Whenitemswithquantitiesotherthan1aresentintoauniversalconnector(suchasdemand or select), they are treated as one item, but the quantity of the item may be used by the block as control information. See below for more information on how universal connectors deal with the incoming items that have quantities other than 1.
All the other blocks deal with items that have quantities other than 1 as a single item, ignoring the quantity associated with it.
☞ The Activity block accepts an item with a quantity greater than 1 as a single item and process it as one unit. To have the items be processed separately, precede the Activity block with a queue, since queues decompose items with quantities greater than 1.
Setting an item’s quantity
A quantity can be assigned to an item in the Create, Set, or Equation(I) blocks.
Set block
In the table in the Set block’s dialog, select _Item quantity in the Property Name column and enter the quantity in the Property Value column or input a value to the Block’s _Item Quantity value input connector. Each item that passes through the Set block will be assigned that quan- tity.
Create block
The default setting in the Create block is that one item is input to the model at each arrival event; this is the most common case when building models. How you specify that a multiple number of items be released at each event depends on which behavior is selected for the Create block:
• Create block is set to “Create items randomly”. Change Item quantity (Q) in the Options to an integer number other than 1. Or input a value to the Create block’s ItemQuantity (Q) value input connector.
• Create block is set to “Create items by schedule”. Enter values in the table’s Item Quantity column for each Create Time field that has arrival times.
For example, assume you want to show that one item arrives randomly approximately every 4 minutes. To do this, use the same settings as in the Car Wash model from the discrete event
Discrete Event

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