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Questions and Answers
Which scheduling method uses the principle of processing the earliest jobs first?
Which scheduling method uses the principle of processing the earliest jobs first?
Throughput measures the proportion of time that the server is busy.
Throughput measures the proportion of time that the server is busy.
False
What does 'U' represent in the context of server utilization?
What does 'U' represent in the context of server utilization?
Proportion of time that the server is busy
The __________ event occurs when the server finishes serving a customer and is ready to serve the next customer.
The __________ event occurs when the server finishes serving a customer and is ready to serve the next customer.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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Which of the following best describes a 'model' in the context of discrete-event simulation?
Which of the following best describes a 'model' in the context of discrete-event simulation?
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An entity in discrete-event simulation refers only to physical objects such as machines or people.
An entity in discrete-event simulation refers only to physical objects such as machines or people.
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What does the term 'event list' refer to in discrete-event simulation?
What does the term 'event list' refer to in discrete-event simulation?
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A duration of time that is known when it begins is referred to as an __________.
A duration of time that is known when it begins is referred to as an __________.
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Match the following components of discrete-event simulation with their correct descriptions:
Match the following components of discrete-event simulation with their correct descriptions:
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In discrete-event simulation, which of the following defines a 'delay'?
In discrete-event simulation, which of the following defines a 'delay'?
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The clock in a discrete-event simulation can only be continuous in nature.
The clock in a discrete-event simulation can only be continuous in nature.
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What does the inter-arrival time refer to?
What does the inter-arrival time refer to?
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The service time can be calculated as the service requirement divided by the server capacity.
The service time can be calculated as the service requirement divided by the server capacity.
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What is the arrival rate?
What is the arrival rate?
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Service rate is defined as the number of customers served per second, assuming no ______ time.
Service rate is defined as the number of customers served per second, assuming no ______ time.
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Match the following queue types with their definitions:
Match the following queue types with their definitions:
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Which of the following options describes service discipline?
Which of the following options describes service discipline?
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The service requirement varies based on the type of service being provided.
The service requirement varies based on the type of service being provided.
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How is the mean inter-arrival time calculated?
How is the mean inter-arrival time calculated?
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The ______ rates are quantified by how many units of work a server can handle per second.
The ______ rates are quantified by how many units of work a server can handle per second.
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Which of the following is an example of service requirement?
Which of the following is an example of service requirement?
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What does TE represent in discrete-event simulation?
What does TE represent in discrete-event simulation?
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In the grocery store example, LQ(t) represents the number of customers being checked out at time t.
In the grocery store example, LQ(t) represents the number of customers being checked out at time t.
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What is the stopping time set for the grocery store simulation?
What is the stopping time set for the grocery store simulation?
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In the event scheduling approach, an arrival event is represented as (A, t) where A indicates __________.
In the event scheduling approach, an arrival event is represented as (A, t) where A indicates __________.
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Match the components of the grocery store example with their descriptions:
Match the components of the grocery store example with their descriptions:
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Which of the following is NOT a component of the grocery store simulation?
Which of the following is NOT a component of the grocery store simulation?
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In the grocery store simulation, an event notice includes the event type and event time.
In the grocery store simulation, an event notice includes the event type and event time.
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What are the two main statistics tracked in scenario 1 of the grocery store example?
What are the two main statistics tracked in scenario 1 of the grocery store example?
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The __________ event represents the stopping condition of the grocery store simulation.
The __________ event represents the stopping condition of the grocery store simulation.
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Which component must the current snapshot contain to continue the simulation?
Which component must the current snapshot contain to continue the simulation?
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In a grocery store simulation, the sum of customer response times is represented by the statistic 'N'.
In a grocery store simulation, the sum of customer response times is represented by the statistic 'N'.
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What are the attributes of a customer entity in the grocery store simulation?
What are the attributes of a customer entity in the grocery store simulation?
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The simulation program’s initialization includes setting the clock to _____ and initializing state variables.
The simulation program’s initialization includes setting the clock to _____ and initializing state variables.
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Match the following statistics with their representations in the grocery store simulation:
Match the following statistics with their representations in the grocery store simulation:
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What happens in the main loop of a generic simulation program?
What happens in the main loop of a generic simulation program?
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Event routines are used to report performance measures at the end of the simulation.
Event routines are used to report performance measures at the end of the simulation.
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What type of events should be removed from the event list during the simulation?
What type of events should be removed from the event list during the simulation?
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To estimate mean response time in the grocery store simulation, it is necessary to collect the sum of customer response times denoted by _____ .
To estimate mean response time in the grocery store simulation, it is necessary to collect the sum of customer response times denoted by _____ .
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Which of the following describes the event scheduling approach?
Which of the following describes the event scheduling approach?
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Study Notes
Chapter 4: Discrete Event Simulation
- This chapter covers discrete event simulation, a type of simulation used in various applications
- The presentation mentions a course called "Discrete Event Simulation" at the "Institut Supérieur d'Informatique et de Mathématiques".
- The course is for level 2 students in the Information Systems (INF) program, in the academic year 2024-2025.
Simulation Model Taxonomy
- A taxonomy of simulation models is presented, categorizing models based on system characteristics
- Models can be categorized as static or dynamic, deterministic or stochastic
- Further categorization distinguishes continuous and discrete models for dynamic systems
- Static models (e.g., Monte Carlo simulations) are a specific type of static, stochastic model.
- Discrete models (discrete-event simulations) represent dynamic systems with discrete state changes.
How to Develop a Simulation Model
- The process of developing a simulation model involves several steps:
- Establishing the goals and objectives
- Creating a conceptual model
- Defining a required specification model
- Developing a computational model
- Verifying the model
- Validating the model
- Simulation development is often iterative.
Outline of Discrete-Event Simulation Topics
- The outline includes key topics for discrete-event simulations:
- Defining discrete-event concepts
- Two example cases (ABC Call Center and Grocery Store)
- Different types of time advance techniques
- Event scheduling
- Manual simulation
- Queuing system simulations (infinite and finite population models)
- Verification and validation of models
- Methods to program simulations
Concepts in Discrete-Event Simulation
- A model is an abstract representation of a real-world system.
- A system is a collection of interacting entities over time (e.g., people, machines, servers in a computer network).
- System states describe variables that capture the information needed to describe the system at any specific time (e.g., occupancy).
- An entity is an object or component of a system (e.g., a customer, a server).
- Attributes are properties of entities (e.g., time, status, other properties).
- Events are instantaneous occurrences that change the system's state (e.g., a customer arrives, a customer leaves).
- The event list is a list of predicted future events in order of occurrence.
- Activities are durations of time of either a specified or unspecified length
- Conditional wait (e.g., waits in lines) are delays whose duration depends on current conditions
- A clock is a variable used for measuring simulated time, either discrete or continuous
Two Pedagogical Examples
- Example 1: ABC Call Center
- Scenario of a computer technical support center
- Goal: Determine the efficiency in response time
- Variables to track: arrival times between calls, service times for workers (Alice, Bob, Chris)
- Example 2: Pancake Manor
- A pancake restaurant in Australia
- Goal: Determine the appropriate number of staff and seating arrangements
- Factors to track: arrival times of customers, group sizes, time of day and service times (ordering, eating, payment)
Components of Discrete-Event Simulation:
- The simulation process is driven by events that change the system state.
- The simulation model advances based on the order of events.
- System states change when events are processed.
- The system requires a time advance algorithm, event scheduling, and event processing for operation
Time Advance Approaches
- Time-Stepping: Advances the clock by fixed increments to process all pending events at each step
- Event Scheduling: Uses an event list to prioritize and execute events in chronological order, thus avoiding unnecessary steps in the simulation cycle
List Processing
- Operations like adding and removing events, and determining which event is next, are performed.
- The system decides the data structure to employ based on the size of the system
- Potential data structures include variables, arrays, files, ordered linked lists, priority queues, binary heaps, and calendar queues
Future Events
- Events like arrivals and service completions occur and are scheduled on the FEL.
- Completion of specific conditions may trigger other simulation events (e.g., reaching 1000 customers)
Manual vs Computer Simulations
- Computerized event-scheduling models hold one snapshot of the current, or partially updated, state in memory.
- New states can only be derived from the previous state, new random variables and the event logic
Single-Channel Queue Example (Grocery Store)
- This focuses on a single checkout queue in a grocery store
- The system comprises queue length, and customer status.
- The simulation uses arrival and departure events; time constraints are included
- A flowchart models the events for arrival and departure
Scenario Analysis (Grocery Store)
- Various scenarios can be simulated (e.g., one check out lane) to assess and determine the number of customers a single check out can handle
- Data collection includes Arrival Times, Service Times,
- Performance metrics like busy time and maximum queue length are calculated
Simulation Program Structure
- Initialization: Initializes variables (clock, system status, counters), event list, and queue.
- Main loop: Continues until a defined termination condition is met. Identifies the next event and updates the system.
- Event Routine: Performs actions associated with a specific event type.
- Report Generator: Summarizes simulation results
Simulation of Queuing Systems
- Queuing system simulations examine systems with queues, including:
- Single server infinite and finite populations
- Tandem queues
Concepts of Arrival and Service
- Arrivals: Time a customer arrives, interval between arrivals, arrival rate (customers per unit of time)
- Service: Time spent by a customer in service, service time distribution, service rate
Typical Performance Measures
- Response time: Time between arrival and departure
- Waiting time: Time customers wait in the queue
- Number of customers in the queue
- Server utilization: Percentage of time the server is busy
- Throughput: Rate at which customers leave the service facility.
Utilization
- Proportion of time in which a server is busy.
- The utilization time is calculated by summing the service times divided by the total time
Throughput
- Rate at which customers leave the service after finishing service (customers/unit time).
Single Server Queue Example
- A model for a single service point and its accompanying queue.
Customer Arrivals (Infinite Population)
- Large number of customers who potentially will always arrive. The patterns of customer arrivals will not change with the system condition
Single Server Queue Model
- Assumptions about interarrival and service times are made for the simulation
Single Server Queue Model (Steps 1-5)
- Describes steps involved for the simulation model (initialization, main loop, arrival event, service event, departure event)
Single Server Queue Model (Output Calculation)
- Mathematical calculations will produce the output (Mean Waiting Time and Mean Number of Customers)
Finite Population Model
- The customer base in the system is fixed and limited, with customers arriving and departing
- Arrivals and departures will depend on earlier service completions
Tandem Queues
- A series of service stages where the output of one becomes the input of the next.
Validation & Verification Strategies
- Verification and validation strategies to check the consistency and accuracy of the results, which may use historical data or analytic solutions to verify the output of the simulation
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Description
Test your knowledge on discrete-event simulation concepts and terminology. This quiz covers key principles including scheduling methods, server utilization, and event definitions. Prepare to match terms with their correct descriptions and understand various components of simulation.
