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Advanced Topics
Messaging in discrete rate models
culate at a certain time. This gives all the other blocks in the model the opportunity to update before the recalculation occurs.
☞ In discrete rate models, blocks from the Value library typically neither post events to the Exec- utive nor receive event messages from the Executive. This has important ramifications on the behavior of continuous blocks in discrete rate models.
Value connector messages
Blocks in a discrete rate model send value connector messages either because a new number is needed by an input connector or because the value of an output connector has changed. These messages request updated information for the input connectors or notify connected blocks that the output value has changed. For example, if a Valve block’s R value input connector is con- nected and the Valve receives a new value at R, the constraining rate on the flow changes. This will cause a recalculation of the set of parameters in the model.
These messages work the same in discrete rate models as in discrete event models. They are discussed fully at “Value input and output connector messages” on page 319.
Item connector messages
Discrete rate models often have portions that are item-based, using blocks from the Item library. The Rate library’s Interchange block also has item connectors; it provides a mechanism for interacting with item-based blocks in a discrete rate model.
Item connector messages (primarily wants, needs, and rejects) use a conversation of mes- sages to propel items from one item-based block to another through the model. The item con- nector messages work the same in discrete rate models as in discrete event models. They are discussed fully at “Item connector messages” on page 321.
Flow connector messages
Flow connectors provide the value of the effective inflow and outflow rates. Flow connector messages cause the effective inflow/outflow rate to be updated for all connected blocks each time the LP calculation determines that the effective rates have changed.
Rate block flow messages
As soon as a block from the Rate library receives a message, if it determines that the effective inflow and outflow rates might change, it initiates a propagation of these messages. This prop- agation of messages is used to define the LP area – the area of the model which could be impacted by the originating block’s change.
Executive block flow messages
When a calculation of a set of effective rates for the LP area has been initiated, the Executive block calculates the new set of effective rates and sends messages to the blocks in order to propagate the results. These message update all the blocks in an affected area with a new effec- tive rate.
Discrete Rate

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