Glossary

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READ FIRST! HOW TO ADD THINGS TO THE GLOSSARY (temporary readme, to be deleted once wiki is finalized!)
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Contents Top · 0–9 · A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

0-9

* (SIGMA function)
Function that makes immediate event execution when placed on an edge.
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A

ASK{X}
Displays the value of expression X during the run and allows you to change it.
Attribute
Characteristic of an entity.
See also Systems.
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B

BET{X,Y}
The SIGMA function for a beta distribution with shape parameters X and Y.
Boolean variable
A variable that equals 1 if it is true and 0 if it is false.
Buffer
The limited waiting space of a queue.
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C

Canceling edge
An edge that cancels the event of the vertex it is pointing at. In SIGMA, a canceling edge by default is represented by a dashed line.
See also edge.
CLK
Variable representing the current value of simulated time.
Conditional edge
An edge that requires a set of conditions to be satisfied before it can execute.
See also edge.
COS{X}
SIGMA function for cosine of the input X.
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D

Dependent (Random variables)
Two random variables are dependent if they are not independent
Discrete event simulation
Simulation of a discrete event system.
See also Discrete Event System Modeling.
Discrete Event System
Systems where the status of the system changes at a particular instant of time.
DISK{F,I}
Reads the I-th number from disk file, F, where I is any valid integer-valued SIGMA expression. If I=0, the file is read sequentially. Data files can be read in any (random) order.
See also Reading Data (and Code) from Your Disk.
Do-loop
TBA
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E

Edge
An arrow between two vertices representing the relationship between those two events.
EG
Acronym for event graph.
Empirical distribution
A distribution computed from observed data.
See also Using Empirical Input Distributions.
Entity
Articles whose interaction make up a system.
See also resident entities and transient entities.
See also Systems.
English translation
See automatic translation of SIGMA models.
ERG
Acronym for event relationship graph.
Event
A change in the state of the system.
Event Canceling
See Canceling Edge.
Event graph
A diagram that graphically captures the events taking place within a system and the relationships among these events.
See also Event Graphs.
Event relationship graph
See event graph.
ERL{X}
SIGMA function for an Erlang distribution with parameter X.
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F

FIFO
Acronym for "first in first out". Queueing methodology where the first entity to start service is the first entity to leave service.
Future events list
The master scheduler of events in a discrete event simulation that contains all of the events that are scheduled to occur in the future.
See also Discrete Event Systems and Simulations.
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G

GET{OPTION;LIST}
Removes a record from the specified LIST according to the OPTION chosen and places its contents in the ENT[] array.
See also Using Ranked Lists.
Graphics (Run mode)
SIGMA Run Mode for which vertices and edges change color as the simulation progresses.
See also Run Modes
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H

High Speed (Run mode)
SIGMA Run Mode that bypasses the graphics in SIGMA and produces an output file.
See also Run Modes
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I

Independent (Random variables)
Two random variables are independent if and only if knowledge of the occurrence of any of these events has no effect on the probability of any other event.
Initialization bias
TBD
See also Simultaneous Parallel Replications.
Initialization condition
Required user inputs necessary to start a simulation run
See also Initial Attributes
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J

Just-In-Time
See Just-In-Time compilation.
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K

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L

LIFO
Acronym for "last in first out". Queueing methodology where the last entity to start service is the first entity to leave service.
LN{X}
SIGMA function for the natural logarithm of an input X.
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M

Max{X,Y}
Gives the maximum of expressions X and Y.
Mean
The arithmetic average of a set of numbers.
MIN{X,Y}
Gives the minimum of expressions X and Y.
MOD{Y,X}
Gives the integer remainder when the value of expression Y is divided by the value of expression X.
Model
A system used as a surrogate for another system.
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N

Node
See vertex.
NOR{X,Y}
Sigma function for a normal distribution with mean X and variance Y.
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O

Option (PUT and GET)
Option for how contents of ENT[] array are placed on the LIST for PUT or removed from the LIST for GET.
See also Using Ranked Lists.
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P

Parameter (Event)
A variable that describes certain characteristics of an entity and is passed as an attribute along edges between vertices.
See also Event Parameters and Edge Attributes.
Phantom Server
A server created by simultaneously scheduled events.
See also REWORK1.MOD.
Priority (edge)
Rank used to break time ties between events scheduled to occur at the same clock time.
Priority (execution)
See Priority (edge)
Priority queue
A queue where certain types of customers are given priority over other types.
Process worldview
A modeling philosophy where the focus is typically on transient entities.
PUT
Places the current contents of the ENT[] array in the LIST according to according to the OPTION chosen.
See also Using Ranked Lists.
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Q

Queue
A line of individuals waiting for service.
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R

Random number seed
Five digit number required to generate a pseudo random number in SIGMA.
See also Random Seed
Reflexive edge
TBD (not in the reader (?)
Resident entity
Entities that are inherent to the system. For example, workers in a car wash.
Rework
The need to process a job again due to a problem with the original processing.
RND
Variable representing a randomly chosen number between zero and one.
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S

SET{X}
Sets all variables (including CLK) to zero and sets the random number seed to X; with no argument, the original stream continues.
SIGMA
Simulation Graphical Modeling and Analysis. ADD MORE HERE.
Single step
SIGMA tool that allows you to watch the simulation as each event is executed.
See also The SIGMA Modeling Environment
See also Run Modes
SIN{X}
SIGMA function for the sine of an input X.
Size (of a variable in SIGMA)
TBD.
State (system)
The state of a system is a complete description of the system and includes values of all attributes of entities, parameters of laws, factors for its policies, time, and what might be known about the future.
State change
A change in a state variable.
State variable
A variable that describes the state of the system being modeled.
Step plot
A type of Output Plot that shows the values of traced variables during a simulation run.
See also Output Plot
STS{X}
Gives the area under the standardized time series for the traced variable X.
See also Output Plot - Trend Detection
System
A collection of entities that interact with a common purpose according to sets of laws and policies.
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T

Tandem queue
A queueing network where customers proceed through successive service operations along a single path.
TAV{X}
The time average of the traced variable, X.
Time (simulation)
TBD.
Time average
An average of taking into account how much simulated time the variable spends at a particular value.
See also TAV{X}.
Time sample variance
TBD. (not in reader (?))
Time series
A sequence of data points, measured typically at successive times
See also Standardized Time Series.
Time tie
Occurs when two events are scheduled to occur at the same time.
Trace (simulation)
A simulation where whenever a value for a random variable is needed by the simulation, it is read from a data file.
See also Trace Driven Simulations.
Trace variable
State variables chosen to be recorded and displayed during a simulation run.
See also Trace Variables.
Transient entity
Entities that enter into and depart from the system with relative frequency. For example, cars in a car wash.
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U

Unconditional edge
An edge that tests the condition (1==1), which is always true, and therefore always executes.
See also edge.
Uniform distribution
In SIGMA, a uniform distribution may be ADD MORE HERE!!
See also uniform distribution.
User (variable)
TBD. (not really in reader, says it's "beyond the level intended for this documentation")
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V

Validation (modeling)
INPUT DEFINITION FROM THE READER HERE.
VAR{X}
Cumulative variance for the traced variable X
Variable
TBD.
Verification (modeling)
The process of testing if the simulation is good.
See also Model Verification.
Vertex
A node in an Event Graph representing an event.
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W

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X

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Y

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Z

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