ROSE-HULMAN INSTITUTE OF TECHNOLOGY Department of Electrical and Computer Engineering EC 300 Signals and Systems BAF, Winter 2004 Introduction to MATLAB Lab 1 Mark A. Yoder and Bruce A. Ferguson Objectives The purpose of this lab is to play with MATLAB, specifically, using its command-line interface. While playing you should learn many of the commands we will be using throughout the quarter. Don’t be afraid to try things. You can’t break it. Specifically, you should achieve the following: • Learn to use the MATLAB command-line interface • Learn basic syntax and command structure • Learn to create signals as arrays associated with a time axis array Pre-Lab 1. The first pre-lab exercise is to get MATLAB and the signal processing toolbox installed on your laptop. (You may use a version of MATLAB already installed from a previous course). MATLAB is available from the tibia server: start_menu>run>\\tibia\public\Apps\Matlab. The signal processing toolbox is available with the network version, or is available in the student edition from the bookstore. Be sure to have MATLAB installed and running before you come into lab. Each student will need a copy and their computer in lab. There will not be time during lab to do the installation. Note: If you are using the network version of MATLAB, you must be connected to the network to use the software. 2. Obtain a laboratory notebook for ECE 300. The use of a used notebook is allowed as long as sufficient space is available for this course’s lab entries. Create a table of contents for ECE 300, and a prelab page for lab 1. Make an entry in your lab notebook indicating the date and time that you and your partner each successfully installed MATLAB. Note: This lab, and all labs, requires recording in a lab notebook. Guidelines are available on the course lab webpage. 3. Read the handout “Simulating Waveforms in MATLAB” before lab. Notes on Using MATLAB MATLAB can be used in two different ways – through the command line interface and using MATLAB scripts. It is important that you know the difference between the two and when to use each. You will practice each in your first two labs in ECE 300. The first lab focuses on the command line interface. The command line interface is the easiest way to use MATLAB, and is the default mode on startup. When you first start MATLAB, you will find that a “command window” opens as part of the MATLAB window. Using this command window, you can enter commands at the prompt (>>) for MATLAB to evaluate. This is convenient when doing simple calculations and getting help. A major disadvantage of the command line interface is that the work you do cannot be saved for future use. Page 1 of 6EC 300 Signals and Systems Fall 2004 Procedure: There are three exercises for today’s lab 1. Play Time – record notes and observations in your laboratory notebook. (Tip – It is always good to compare your observations with your expectations, or theory and measurement, especially when they disagree. There is no need to write things down for obvious steps.) (a) Explore the MATLAB help capability. Try the following (type at the command prompt – note that the text following the % is a comment; such text may be omitted without altering the command function): help % this is the basic help command help plot helpwin plot % opens a help window on the plot command help colon lookfor filter % keyword search (b) Use MATLAB as a calculator. Try the following: pi*pi-10 sin(pi/4) ans^2*3 % ans holds the last result (c) Practice variable name assignment in MATLAB. Try the following: x = sin(pi/5); cos(pi/5) % assigned to what? y = sqrt(1-x*x) ans NOTE: The semicolon at the end of a statement will suppress the echo to the screen. (d) Experiment with vectors in MATLAB. Think of the vector as a set of numbers in a one-dimensional array. Try the following: kset = -3:11; kset length(kset) cos(pi*kset/4) % compute cosine Using your lab notebook and a pen, explain using mathematical expressions how the last example computes the different values of cosine. The cos command introduces the concept of implicit type assignment. MATLAB senses that the cosine argument contains a vector, so it implicitly creates a vector to store the results of the cos command. The length of the cos vector is automatically set equal to the length of the kset vector. Page 2 of 6EC 300 Signals and Systems Fall 2004 (e) Create a time vector in MATLAB. Try the following: helpwin linspace t = linspace(0,0.1,100); t x = cos(2*pi*20*t); % compute cosine x (f) Make sure that you understand the colon notation. In particular, explain what the following MATLAB code will produce: help colon jkl = 2:4:17 jkl = 99:-1:88 ttt = 2:1/9:4 tpi = pi*[2:-1/9:0] (g) Extracting and/or inserting numbers in a vector is very easy to do. Consider the following definition: x = [ones(1,3),[5:2:13],zeros(1,4)] x(6:9) Explain the result echoed from x(6:9). Now write a single statement that will replace x(6:9) in the existing vector x with zeros. Instructor Verification (see last page) (h) Loops can be used in MATLAB, but they are NOT the most efficient way to get things done. When efficiency is important, such as when dealing with very large vectors, it is better to avoid loops and use the vector notation instead. However, in this course, where we are beginners, the for loop is sufficient. Here is a loop that computes values of the sine function. (The index of x() must start at 1.) x = []; % initialize the x vector to a null for i=0:7 x(i+1)=sin(i*pi/4) end x Rewrite this computation without using the loop. Instructor Verification (see last page) (i) Complex numbers are natural in MATLAB. All of the basic operations are supported. Try the following: z = 3+j*4 conj(z) abs(z) angle(z) real(z) imag(z) exp(j*pi) Page 3 of 6EC 300 Signals and Systems Fall 2004 exp(j*[pi/4 - pi/4]) (j) Plotting is easy in MATLAB, for both real and complex numbers. The basic plot command will plot a vector y versus a vector x. Try the following: x = [-3 -1 0 1 3]; y = x.*x-3*x; plot(x,y) z=x + x*j plot(z) % complex values can be plotted subplot(2,1,1), plot(x,y) subplot(2,1,2), plot(z) Use helpwin arith to learn how the operation x.*x works. Compare to matrix multiplication x*x. This “dot” arithmetic is an extremely important concept in MATLAB. (k) Run the MATLAB demos; enter demo and
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