GPSS/H Notes

GPSS/H Notes

Discrete-Event simulation Modeling is used to evaluate proposed new systems and proposed changes to existing systems when actual changes in the system would be impractical. In addition, the process of modeling a system gives us greater understanding of the modeled system.

Installing GPSSH

1) Put the student version of the disk in your disk drive.

2) From Windows Explorer (or FileManager) double-click on INSTALL.EXE

3) Press space to continue

4) Select Drive C

5) Accept directory \GPSSH as directory unless you understand enough to change this.

6) Have the proposed modifications to AUTOEXEC.BAT shown on your screen where you can ignore them.

7) In Windows explorer Options uncheck hide file extensions of registered programs.

Using GPSSH

At UVI on STT GPSSH is located in the directory J:\dosapps\gpssh. To get started

Command	Comment
Launch MS-DOS Prompt	You’ll probably find this in the accessories area.
J:	At UVI switch to J drive. At home you will probably find GPSSH on the C: drive.
CD \dosapps\gpssh	At UVI change to gpssh directory. At home you will probably use \gpssh
DIR	Make sure that you’re in the right spot by looking for the GPSSH.EXE file, this command is optional.
gpssh A:p1.gps	Run the program using the source file p1.gps located on drive A. Substitute your file name for p1.gps

Editing your Programs

You must use a text editor. Notepad can cause problems because it has a bad habit of adding a hidden .txt extension that gpssh doesn’t understand. Advanced Word processors can be used but you must, "SAVE AS" text. Most advanced word processors will not let you run the program until you have closed its window. Edit Pad is a good choice because it’s small, shows cursor position and doesn’t lock the file. Be sure to put commands in the proper column (usually commands start in column nine). http://tucows.pdnt.com/adnload/dleditpad.html

General Notes

Files must be in the format xxxxxxxx.GPS . That .GPS ending is critical and the file must be equal to or shorter than eight characters long.

When GPSS/H runs a model, the program examines the file for errors then compiles it and creates an output file in the format xxxxxxxx.LIS with the same model name.

GPSS/H views the world as transactions (entities) moving from area to area called blocks. Each area represents an action that can change the entity.

Basic Elements of GPSSH

Transactions	Nicknamed XACTS. Transactions are created by the GENERATE or START statements and destroyed by the TERMINATE statement. Transactions compete for resources and must wait if required resources are busy. Transactions may require more than one resource. Transactions often represent a person (going through a line) or object (car being assembled). Transient transactions leave the system. Permanent Transactions (Entities) never leave the system. Transactions can have attributes (number of items to process or type). Transactions can interact with each other. In example, Passengers waiting to get on a train and trains waiting to get to the station.
Resources	Resources are static permanent entities. (assembly workers, tools, machines) It is occasionally desirable to substitute a transaction for a resource. Facility Resources are a single resource. (A single cashier) Storage Resources are parallel Facility Resources.
Blocks	Blocks describe how a transaction moves through the system and is processed.

Program Commands

Most code is paired (ADVANCE is the exception).

Commands must be started on the ninth column.

Put operands in column 20.

There should be no spaces in the operands not even after the commas.

The first space after the operands start is assumed to start the line comments.

Be sure to keep your time units consistent.

Named objects must have names that are eight characters or shorter.

Command	Comments
1 2 3 123456789012345678901234567890123456
COMMAND OPERAND COMMENT
SIMULATE <Program> END	Start and stop the code. Just put these in at the beginning and the end of your command.
START A	Number of Units to Create. When this number of units is terminated or the maximum number of generated items is created, the program ends.
GENERATE A,B,C,D TERMINATE A	GENERATE A,B,C,D A Average Time B Spread of Time C Start Time D Max # of Transactions TERMINATE A # of Transactions to Remove This command can be used to generate transactions or as "dummy code" to time a sequence.
ADVANCE A,B	Hold Transaction for Period of Time A Average Time B Spread of Time
SEIZE Name <possible code ie advance> RELEASE Name	Capture/Free a named facility.
STORAGE S(Name),#/S(Name2),# ENTER Name <possible code ie advance> LEAVE Name	Capture/Free one or more units of storage. Number of units is defined at the top.
REALLOCATE COM,32720	Reallocates memory up to 32720 units. The default allocation is 10000 units. Try this command if your model is not running and your sure that you’re terminating all your transactions properly.
QUEUE Name <possible code ie advance> DEPART Name	Collect Statistics on a transaction flow. Most often used in the QUEUE ENTER/SEIZE DEPART format.

Printing Work

Be sure to print your work in columnar font such as courier.

You must have your name, the assignment number and the problem number in the comment section.

Use lots of so that I can understand what you are trying to do.

Remove unnecessary parts of the .LIS output so that your output is no more than two pages and preferably just one page.

Staple your work