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Contents 1 Description 2 State Variables 3 Vertices 4 Initialization Conditions 5 Event Relationship Graph 6 English Translation 7 Comments

Description

FLOWPROC.MOD is an example of changing the visual representation of the simulation. In FLOWPROC.MOD, the vertices have all been changed to flowchart symbols to create a process flowchart.

Double clicking on a vertex and changing its shape from a circle to a desired flowcharting symbol in the drop-down menu is all that is required to create process flow charts.

State Variables

State Variables in FLOWPROC.MOD

Variable Name	Abbreviation	Variable Description	Size	Type
QUEUE	Q	Number of cars in line	1	Integer
SERVERS	S	Number of machines available	1	Integer

Vertices

Vertices in FLOWPROC.MOD

Vertex Name	Vertex Description	State Changes
RUN	The simulation is started	None
ENTER	Cars enter the line	Q=Q+1
OPEN	A car wash stall is open, start wash	None
START	Service starts	S=S-1, Q=Q-1
WASH	Wash car	None
LEAVE	Cars leave	S=S+1

Initialization Conditions

Initialization Conditions in FLOWPROC.MOD

Variable	Description
QUEUE	Initial number of cars in line
SERVERS	Initial number of available servers

Event Relationship Graph

English Translation

An English translation is a verbal description of a model, automatically generated by SIGMA.

The SIGMA Model, FLOWPROC.MOD, is a discrete event simulation. 
It models AN AUTOMATIC CARWASH - Process Flow.

I. STATE VARIABLE DEFINITIONS.

For this simulation, the following state variables are defined:

QUEUE: NUMBER OF CARS IN LINE   (integer valued)
SERVERS: NUMBER OF AVAILABLE MACHINES   (integer valued)

II. EVENT DEFINITIONS.

Simulation state changes are represented by event vertices (nodes or balls) in a SIGMA graph.  
Event vertex parameters, if any, are given in parentheses. Logical and dynamic relationships 
between pairs of events are represented in a SIGMA graph by edges (arrows) between event vertices.  
Unless otherwise stated, vertex execution priorities, to break time ties, are equal to 5.

1. The RUN(QUEUE,SERVERS) event occurs when THE SIMULATION RUN IS STARTED.
   Initial values for, QUEUE,SERVERS, are needed for each run.
   After every occurrence of the RUN event:
   Unconditionally, THE CAR WILL ENTER THE LINE;
   that is, schedule the Enter() event to occur without delay.

2. The Enter() event occurs when CARS ENTER THE LINE.
   This event causes the following state change(s):
   QUEUE=QUEUE+1
   After every occurrence of the Enter event:
   Unconditionally, THE NEXT CUSTOMER ENTERS IN 3 TO 8 MINUTES;
   that is, schedule the Enter() event to occur in 3+5*RND time units.
   (Time ties are broken by an execution priority of 6.)
   If SERVERS>0, then THERE ARE AVAILABLE SERVERS TO START WASHING THE CAR;
   that is, schedule the Open?() event to occur without delay.

3. The Start() event occurs when SERVICE STARTS.
   This event causes the following state change(s):
   SERVERS=SERVERS-1
   QUEUE=QUEUE-1
   After every occurrence of the Start event:
   Unconditionally, THE CAR WILL BE IN SERVICE FOR 5 MINUTES;
   that is, schedule the Wash() event to occur in 35*TRI{.5} time units.
   (Time ties are broken by an execution priority of 6.)

4. The Leave() event occurs when CARS LEAVE.
   This event causes the following state change(s):
   SERVERS=SERVERS+1
   After every occurrence of the Leave event:
   If QUEUE>0, then THERE ARE CARS IN QUEUE, START SERVICE FOR THE NEXT CAR IN LINE;
   that is, schedule the Start() event to occur without delay.

5. The Open() event occurs when a carwash stall is open, start wash.
   After every occurrence of the Open? event:
   Unconditionally, schedule the Start() event to occur without delay.

6. The Wash() event:
   After every occurrence of the Wash event:
   Unconditionally, schedule the Leave() event to occur without
   delay.

Comments

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