Page 183 - ExtendSim User Guide
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Routing 157
Items from several sources
Math (Value > Math)
Performs a mathematical operation, such as addition or subtraction, that can be used with Item library blocks to control the flow of items in a portion of the model.
Max & Min (Value > Math)
Outputs the minimum or maximum value found among its input connectors. Can be used with Item library blocks to control the flow of items in a portion of the model.
Items from several sources
Depending on your modeling needs, you may want to merge different streams of items into one stream of individual items, select one item from several for routing or processing, or join sepa- rate items into a single item.
• To merge streams of items from several sources into one stream, where each item remains separate and retains its unique identity, use the Select Item In or Throw Item and Catch Item blocks. You then typically direct the single stream into a queue. For example, you can use this to represent traffic merging into one lane or people accessing one hallway from several offices. A Select Item In block is used to:
• Merge streams of items in the “Merging Inputs model” on page 159.
• Directitemsrequiringmoreprocessingin“Cumulativeprocessingtime:timesharing” on page 185.
• Reroute preempted items in “Preemption” on page 192.
Those models use the Select Item In block to route items. The section “Throw Item and Catch Item blocks for merging item streams” on page 160 illustrates using a Catch Item block to merge multiple streams of parts into one stream.
• Toselectanitemforprocessingfromseveralsourcesbasedonsomedecision,usetheSelect Item In block. The decision can be a logical decision (choose every other item to route to the top waiting line) or it can be based on some characteristic of the item (get the item with the highest priority). The specifications for the decision are determined by the entries you make in the dialog of the Select Item In block and are modified by blocks connected to its “select” input connectors. Using the Select Item In block to choose specific items is shown in “Bal- ancing multiple input lines” on page 159.
• To join items from various sources and process them as one unit, use a Batch block, as described in “Batching” on page 208. This is most common when modeling manufacturing processes or packaging operations where subassemblies are joined together. It is also used when two or more items need to be temporarily associated with each other for processing or routing, such as a clerk processing an order. Note that batching differs from using the Select Item In and Select Value In blocks, which only merge streams of items so that items remain separate and are processed separately.
☞ To merge streams of items from one hierarchical layer into one stream at a different hierarchi- cal layer, you can add connectors to the hierarchical block or use the Throw Item and Catch Item blocks, at shown on page 160.
Discrete Event

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