Page 162 - ExtendSim User Guide
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Items, Properties, and Values
Item properties
tutorial: in the Create block select the Exponential distribution and enter Mean: 4; in its Options tab leave Item quantity (Q): 1. To show that 2 car/items arrive every 4 minutes, keep the settings at Exponential with a mean of 4, but enter Item quantity (Q): 2. The block will now output one item with a quantity of 2 approximately every 4 minutes.
As discussed in “How blocks treat items with quantities other than 1” on page 135, the blocks that follow the Create block determine how an item with a quantity greater than 1 is treated. For instance, if an item with a quantity of 2 goes directly into a Queue or Resource Item block, it will be split into two items each with a quantity of 1. However, if the item goes directly into an Activity block, it will be treated as a single item with a quantity of 2. In most cases, you will want to follow the Create block with a Queue, which will decompose the item into two sepa- rate items.
☞ In most cases, you probably will not want to generate more than one item at each event. For example, rather than inputting 2 items every 4 minutes as discussed above, you would proba- bly want to generate 1 item every 2 minutes. This is because, unless they are inside a container of some sort, it is not common to see two items arrive at exactly the same time; items are more likely to arrive at slightly different times.
Quantities model
For example, assume you will receive 500 items a week, but that almost all of them are received on Wednesday. In this case, there are five arrival events (one event each on days 1 through 5), each with an item quantity of either 50 or 300.
This Quantities model is similar to the Scheduled Intervals model from page 124, except each item the Create block generates has a quantity greater than 1 and the Activity processes 5 items at a time.
The dialog of the Create block is set to Create items by schedule. The arrival times (Create Time) and the number of items arriving at the scheduled time (Item Quantity) are entered in the table, which has been cloned onto the model worksheet.
The table indicates that on the third day (Wednesday) 300 items arrive but that 50 items arrive on each of the other days.
Quantities model
The Create block outputs an item with a quantity greater than 1 as if it were a group of items all arriving at the same time. When the item goes to a Queue block, it becomes multiple copies of itself. In this example, as each item is sent from the Create block to the Queue block, it will become either 50 or 300 units, depending on its quantity.
Running the model shows that the Create block creates 5 items, but that 500 items have arrived to the Queue.
Discrete Event

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