ROSE HULMAN INSTITUTE OF TECHNOLOGY Department of Electrical and Computer Engineering EC 300 Signals and Systems Winter 2004 BAF MATLAB Scripts and Functions Lab 2 Mark A Yoder and Bruce A Ferguson Objectives The purpose of this lab is to learn to write program files in MATLAB While working through this lab you should learn many of the commands we will be using throughout the quarter In addition you will learn to create MATLAB programs which we will use reuse and modify throughout the term Use the help command often and early Specifically you should achieve the following Learn the purpose of MATLAB scripts and functions aka m files Learn to create a script file for performing repeated operations Learn to create functions for custom operations Learn to properly graph data from various sources Pre Lab Create a working directory for you MATLAB work in this class You should create a MATLAB directory with folders for ECE 300 Class and ECE 300 Lab 2 Read the following notes and write a good definition of the path function variable used in MATLAB Type helpwin path for details about the current path setting 3 Indicate how directories are added to the path Add the directories you have created to the path variable Enter this information into your lab notebook and turn a photocopy in as instructed 1 Notes on Using MATLAB MATLAB can be used in two different ways through the command line interface and using MATLAB scripts This second lab focuses on the use of MATLAB programs The second method of interfacing is by writing MATLAB programs called scripts or m files These are programs written in MATLAB s command language the same as is used in the command window In the last lab you typed a sequence of commands in a specific order to achieve some more complex result such as plotting sinusoids Each command had a specific purpose and the order was important However one big problem with the method used in that lab was that you could not save the sequence of commands that you used MATLAB programs allow you to save a sequence of commands for reuse and modification The usual structure of a MATLAB program is similar to that of other programming languages a main program is written filename m and this program can call functions saved in other files function name m The main program is where you organize your work into a coherent flow Functions are used to program repeated command sequences so that your main program can be neater and smaller Every command you type in the command line interface window is actually a MATLAB function Both the main program and functions are called m files but they have slightly different structures Page 1 of 7 EC 300 Signals and Systems Fall 2004 It is suggested that you use the MATLAB script editor to create and modify your m files The editor can be accessed from inside MATLAB File New M File Be sure to save the file before you run it If you do not MATLAB will use the previous version of the file which it has stored in memory Simply type the filename without the m from the command line to run the program MATLAB references the script program only by its filename so choose a name that has meaning Seventeen files named testx make for a confusing lab exercise The files you create and save are stored in the directory shown in the current directory window just above the command window Be sure to create a directory for your ECE 300 labwork and navigate to that directory using the browse button ellipses to the right of the current directory window MATLAB can access any file stored in its path variable The path is a list of directories that MATLAB has been told to look into to find commands and files When you type a command burgerflip in the command window MATLAB looks through its path to find a file named burgerflip m and then executes it Finally when you save a function MATLAB will know the function only by its filename Even if your function definition in the first line of the m file has something different listed as the command name the filename in which you store the function is MATLAB s official reference So when you call the function from either the command window or an m file you must use the name of the file the function is stored in It is obviously good practice to make both the file name and the function definition line use the same name Procedure There are three exercises for today s lab 1 Script file basics a Use the MATLAB editor File New M File to create a program file called sintest m containing the following lines t 2 0 05 3 x sin 2 pi 0 789 t plot a sinusoid plot t x grid on title Test Plot of Sinusoid xlabel Time s Save the file MATLAB cannot access your programs or functions until they are saved from the editor Creating a program file in this fashion allows for easy storage of a number of commands as a MATLAB program The program file is also called an M File or a script The program will be stored in the current directory indicated in the MATLAB window Page 2 of 7 EC 300 Signals and Systems Fall 2004 Run your function from MATLAB by typing its name sintest at the MATLAB prompt note that sintest must reside in MATLAB s search path Verify that the program produces the expected results b You have now created your first MATLAB program Type type sintest at the command prompt to see the file you have created c Edit sintest m to add a line containing the hold on function type help hold for more information followed by another plot command to add a plot of 0 5 cos 2 pi 0 789 t to the plot created above Add a final line to your program containing hold of Note that you must save sintest m in order for MATLAB to access the updated program Instructor Verification see last page 2 MATLAB Functions MATLAB commands typed at the command line interface are simply functions In this exercise we will learn to create various types of functions a Create a simple function with no arguments Type the following lines and save them in a file called greeting m Save the file and test it at the command line This function is just a small program similar to your main program with one major difference function greeting disp Hello world test variable 3 14159 Note that the first line of the function file begins with the word function followed by the function name This first line differentiates a function from a script regular program a script does not contain the function line It is important that you make the function name the same as the filename you save it in An important difference between a script
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