Entity Input Switch

Switch input entities

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Libraries:
SimEvents

Description

A typical scenario in which you might use an input switch is when multiple sources of entities feed into a single queue, where the sequencing follows specific rules. For example, users of terminals in a time-shared computer submit jobs to a queue that feeds into the central processing unit, where an algorithm regulates access to the queue so as to prevent unfair domination by any one user.

Note

If you want to merge message or entity paths and generate code for your component interface, use the Simulink^® Message Merge block. Message Merge block's behavior is the same as the Entity Output Switch block with Active port selection parameter set to All.

For an example, see Generate Entities When Events Occur.

Combine Entity Paths

You can merge multiple paths into a single path using the Entity Input Switch block with the Active port selection parameter set to All. Merging entity paths does not change the entities themselves, just as merging lanes on a road does not change the vehicles that travel on it. In particular, the Entity Input Switch block does not create aggregates or batches.

Here are some scenarios in which you might combine entity paths:

• Attaching different data — Multiple entity generator blocks create entities having different values for a particular attribute. The entities then follow a merged path but might be treated differently later based on their individual attribute values.

• Merging queues — Multiple queues merge into a single queue.

• Connecting a feedback path — A feedback path enters the same queue as an ordinary path.

Sequence Simultaneous Pending Arrivals

The Entity Input Switch block does not experience any collisions, even if multiple entities attempt to arrive at the same time. The categories of behavior are as follows:

• If the entity output port is not blocked when the entities attempt to arrive, then the sequence of arrivals depends on the sequence of departure events from blocks that precede the Entity Input Switch block.

  Even if the departure time is the same for multiple entities, the sequence might affect the system's behavior. For example, if the entities advance to a queue, the departure sequence determines their positions in the queue.

• If pending entities are waiting to advance to the Entity Input Switch block when its entity output port changes from blocked to unblocked, then the entity input ports are notified of the change sequentially. The change from blocked to unblocked means that an entity can advance to the Entity Input Switch block.

  If at least two entities are waiting to advance to the Entity Input Switch block via distinct entity input ports, then the notification sequence is important because the first port to be notified of the change is the first to advance an entity to the Entity Input Switch block.

Select Arrival Path

The Entity Input Switch block allows arrival of entities at its ports. The selected entity input port can change during the simulation.

You can also select the criterion for switching between input ports.

• Select Round robin to select ports in a round robin fashion.

• Select From control port to let the control port determine the selected port.

• Select Equiprobable to let the block randomly select any port with equal probability.

Examples

Generating and Initializing Entities

Different ways to generate and initialize entities and their attribute values.

• Open Model

Comparing Queuing Strategies

Have you ever been in a supermarket checkout and wondered why you are in the slowest line? This example shows how queuing systems can be modeled in SimEvents for this type of application. Two parallel versions of a simple model of a four register supermarket counter are presented - one that uses four separate queues and one with a single "serpentine" queue that feeds all registers.

• Open Model

Ports

Input

Port_1 — Input entity

scalar | vector | matrix

Input entity port for entities entering the block.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | enumerated | bus | fixed point

Port_2 — Input entity

scalar | vector | matrix

Input entity port for entities entering the block.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | enumerated | bus | fixed point

control — Incoming control entity

scalar

Input control port for the incoming control entity that determines the input port for the entities arriving at the block.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Output

Port_1 — Output entity

scalar | vector | matrix

Output entity port for entities exiting the block.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | enumerated | bus | fixed point

Parameters

Number of input ports — Specify the number of input ports

2 (default) | scalar

Determines how many entity input ports the block has.

Programmatic Use

Block Parameter: NumberInputPorts

Type: character vector

Values: '2' | scalar

Default: '2'

Active port selection — Specify the active input port

All (default) | Switch

Specify the active input port to allow arrival of entities at all ports or one port at a time. Select All to combine entity paths and allow arrival of entities at all ports. Select Switch to allow arrival of an entity at only one port at a time.

Programmatic Use

Block Parameter: ActivePortSelection

Type: character vector

Values: 'All' | 'Switch'

Default: 'All'

Switching criterion — Specify input port switch criterion

Round robin (default) | From control port | Equiprobable

Select the criterion for switching between input ports.

• Select Round robin to select ports in a round robin fashion. Set the initial port in the Initial port selection.

• Select From control port to let the control port determine the selected port. A control port will appear to input an anonymous entity carrying data with a value greater than 0, and smaller than or equal to the number of input ports to determine the active port.

• Select Equiprobable to let the block randomly select any port with equal probability. Set the Seed to generate a random number and to determine the active input port.

Programmatic Use

Block Parameter: SwitchingCriterion

Type: character vector

Values: 'Round robin' | 'From control port' | 'Equiprobable'

Default: 'Round robin'

Initial port selection — Specify the initial input port for entity entry

1 (default) | scalar

Specify initially which port allows arrival of an entity.

Programmatic Use

Block Parameter: InitialPortSelection

Type: character vector

Values: '1' | scalar

Default: '1'

Seed — Specify the seed for the random number generator to determine the input port

23453 (default) | scalar

Specify the seed for the random number generator to determine the input port.

Dependencies

This parameter is visible when Switching criterion is set to Equiprobable.

Programmatic Use

Block Parameter: Seed

Type: character vector

Values: '23453' | scalar

Default: '23453'

Version History

Introduced in R2016a