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To depart from one block and arrive immediately at another block. An entity advances from block to block during a simulation.
Entrance of an entity to a block via an entity input port. Arrival is the opposite of departure.
Data associated with an entity.
For example, an entity might be associated with a size, weight, speed, or part number.
The state of an entity input port that permits entities to arrive at the block.
For example, when a Single Server block is empty, its entity input port is available. When the block is busy serving, its entity input port is unavailable.
The state of an entity output port when an entity is trying to depart via the port and the port connects to an unavailable entity input port of another block.
For example, consider a FIFO Queue block whose entity output port is connected to the Single Server block's entity input port. Suppose the queue contains one entity. The queue's entity output port is blocked if the server's entity input port is unavailable, and not blocked if the server's entity input port is available. If the queue is empty, then its entity output port is not blocked because no entity is trying to depart.
An entity that forms part of a composite entity.
An entity that comprises one or more entities as subordinate parts. The parts are called component entities.
Exit of an entity from a block via an entity output port. Departure is the opposite of arrival.
A subsystem containing time-based blocks that is called at the exact time of each qualifying event, rather than at times suggested by the time-based simulation clock. For the Discrete Event Subsystem block, qualifying events are signal-based events; for an appropriately configured Function-Call Subsystem block, qualifying events are function calls.
For example, the subsystem might contain blocks that end the simulation if the length of a queue exceeds 100, and might be configured so that the subsystem executes only at the exact moments when the queue reports an increased length.
An abstract representation of an item of interest in a discrete-event simulation. The specific interpretation of an entity depends on what you are modeling. Entities can carry data, known as attributes.
For example, an entity could represent a packet in a communication network, a person using a bank of elevators, or a part on a conveyor belt.
An input port at which an entity can potentially arrive. An entity input port can be available or unavailable; this state, which can change during the simulation, helps determine whether the port actually accepts the arrivals of new entities.
An output port from which an entity can potentially depart. An entity output port can have a state of blocked or not blocked; this state, which can change during the simulation, determines whether the port's attempt to output an entity is successful.
A connection from an entity output port to an entity input port, depicted as a line connecting the entity ports of two blocks. An entity path represents the equivalence between an entity's departure from the first block and arrival at the second block. The connection line depicts a relationship between the two blocks.
An entity path is in active use by an entity only at zero or more discrete times during the simulation. By contrast, a connection line between signal ports represents a signal that has a well-defined value at all times during the simulation.
An entity input port or an entity output port.
A real number associated with an entity, used to determine its sequence in a priority queue.
Contrast with event priority.
A kind of discrete event subsystem that is called at the exact time of each entity departure from a block or blocks, rather than at times suggested by the time-based simulation clock. See Creating Entity-Departure Subsystems for details.
An instantaneous discrete incident that changes a state variable, an output, and/or the occurrence of other events. The prototypical events are arrivals and departures of entities.
Examples of events are the generation of a new data packet in communications, the exit of a person from an elevator, and the placement of a new part on a conveyor belt.
The internal list of all events that are scheduled for the current time or future times.
For example, when a server begins its service time on a specific entity, the application inserts an entry into the event calendar for the completion of service on that entity at a future time. In a system representing elevator passengers, this event calendar entry might represent the event whereby a specific person in an elevator reaches the desired floor.
A positive integer associated with an event, used to sequence the processing of simultaneous events. Simultaneous events having distinct numerical event priorities are processed in ascending order of the event priority values.
Contrast with entity priority.
Conversion of one event into another. The result of the translation is often a function call, but can be another type of event. The result of the translation can occur at the same time as, or a later time than, the original event.
A signal that can change in response to discrete events. For example, the signal representing the number of entities in a queue changes upon each arrival at or departure from the queue.
A simulation that permits the system's state transitions to depend on asynchronous discrete incidents called events.
A discrete invocation request carried from block to block by a special signal called a function-call signal. A function-call event is also called simply a function call.
The time interval between successive generations, as in a Time-Based Entity Generator block.
A signal input port that is designed for observing signal values. Contrast with notifying port.
A signal input port that notifies the preceding block when a certain event has occurred. When the preceding block is the Event-Based Random Number block, it responds to the notification by generating a new random number.
For example, the t input port of a Single Server block is a notifying port; when connected to this port, the Event-Based Random Number block generates a new random number each time it receives notification that an entity has arrived at the server.
An entity that tries and fails to depart from a block. The failure occurs because the entity output port through which the entity would depart is connected to an unavailable entity input port of another block.
The replacement of an entity in a server block by an entity that satisfies certain criteria.
A signal input port that listens for updates or changes in the input signal and causes an appropriate reaction in the block possessing the port. For example, the p port on an Input Switch block listens for changes in the input signal; the block reacts by selecting a new entity port for potential arrivals.
An update in the value of a signal that is connected to a block configured to react to signal updates. The updated value could be the same as or different from the previous value.
An input or output port that represents a numerical quantity that changes over time and that is defined for all times during the simulation. Unlike an entity port, a signal port has no state and does not have entity arrivals or entity departures.
A sample time hit event, value change event, or trigger event.
Events that occur at the same value, or sufficiently close values, of the simulation clock. Events scheduled on the event calendar for times T and T+Δt are considered simultaneous if 0 ≤ Δt ≤ 128*eps*T, where eps is the floating-point relative accuracy in MATLAB® software and T is the simulation time.
For example, in a D/D/1 queuing system where the arrival rate equals the service rate, an entity generation event and a service completion event are simultaneous. Parameters in the model determine which of these events occurs first, though the clock has the same value in both cases.
A simulation in which state transitions depend on time.
For example, a simulation based solely on differential equations in which time is an independent variable is a time-based simulation.
An event that causes an entity to depart via a special output port when the entity has exceeded a previously established time limit. Use the Schedule Timeout block to schedule a timeout event for each arriving entity. Optionally, use the Cancel Timeout block to remove a timeout event from the event calendar before the event occurs. See Forcing Departures Using Timeouts for details.
The duration between an entity's arrival at a Schedule Timeout block and the scheduled time of the entity's timeout event. See Forcing Departures Using Timeouts for details.
A rising edge or falling edge of a signal. A rising edge is an increase from a negative or zero value to a positive value (or zero if the initial value is negative). A falling edge is a decrease from a positive or a zero value to a negative value (or zero if the initial value is positive).
A trigger edge in a signal that is connected to a block configured to react to trigger edges.
A signal whose trigger edges are used to invoke a behavior during the simulation.
The state of an entity input port that prevents entities from arriving at the block.
For example, when a Single Server block is empty, its entity input port is available. When the block is busy serving, its entity input port is unavailable.
An increase or decrease in the numerical value of a signal that is connected to a block configured to react to relevant changes.
A value that an event-based signal assumes at an instant in time but that does not persist for a positive duration.
For example, when a full N-server advances one entity to the next block, the statistical signal representing the number of entities in the block assumes the value N-1. However, if the departure causes another entity to arrive at the block at the same time instant, then the statistical signal assumes the value N. The value of N-1, which does not persist for a positive duration, is a zero-duration value. This phenomenon occurs in many situations; see Working with Multivalued Signals for details.
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