Introduction to Matlab IIIntroduction to Matlab II

EE 2303 Lab

                                                     

Basic Matlab Review

Data file input/output string, char, double, struct Types of

variables load, save directory/workspace data file

movement

Navigation/workspace commands clear – clears workspace of all variables close all – close all figure-windows Up-arrow – scroll through recently used command

Basic Matlab Review Fundamentals of matrix computing

[ ], Brackets are used to form vectors and matrices

{ }, Curly braces are used in cell array assignment

( ), ParenthesesEnclose arguments of functionsEnclose subscripts of vectors and matricesIndicate precedence in arithmetic

expressions

Basic Matlab Review Plotting functions

plot(), stem() 1-dimensional graphingmesh(), imagesc() 2-dimensional

visualization

Creating Arrays cell(M,N) create M-by-N cell array of

empty matrices Individual cells can be any matlab data type Enables matrices with mixed elements

e.g.

Creating Arrays zeros(M,N) create M-by-N zeros matrix

ones(M,N) create M-by-N ones matrix

User Interface Commands

More user-friendly Looks slicker Principal UI commands

uigetfile() – retrieve files questdlg() – input logical buttons inputdlg()– input values

uigetfile() Retrieves file via browser windowEx: [audio_input, pathname] = uigetfile('*.wav', 'Please select a wav-file');

inputdlg() Parameter input dialog outputs cell arrayEx: lpdlg = inputdlg({'Enter cutoff frequency(in Hz)'},'Low Pass Filter Parameters',1,{'1000'});

questdlg() Asks question – Yes-No-Cancel by defaultEx: isdlg = questdlg('Would you like to listen to your input signal?', 'Input sound');

guide GUI Design Environment

Alter .fig files

Design self-contained gui’s

Debug Mode Used for scripts

Complex NumbersFor a complex signal x of size N…

real() -- outputs real components imag() – outputs imaginary components abs() – yields magnitude angle() – yields phase of signal

By default, i and j are both set to sqrt(-1)

Z = x + j*y can also be written:

Z = (x,y) essentially a 2d matrix

Discrete Fourier Transform

Used to find frequency response of digital signals Discrete signal input DFT discrete

frequency response Matrix form of DFT:

eWNknjkn

N

/2

1

0

N

n

kn

NWnxkX

FFT Example

Create an example signal:

t = 0:0.001:0.6;x = sin(2*pi*50*t) + …

sin(2*pi*120*t);y = x + 2*randn(size(t));plot(1000*t(1:50),y(1:50))title('Signal Corrupted with

Zero-Mean Random Noise')xlabel('time (milliseconds)')

FFT Example

Now find the frequency response using the DFT

Y = fft(y,512);Pyy = Y.* conj(Y) / 512;f = 1000*(0:256)/512;plot(f,Pyy(1:257))title('Frequency content of

y')xlabel('frequency (Hz)')

Lab Exercise The goal of this lab

is to expand your Matlab repertoire through: Debugging a faulty

script Creating a user

interface script Creating an audio-

Input script

Approximating RealityApproximating RealityEE 2303 Lab

References:

Oppenheim, Schafer. Discrete-Time Signal Processing. 2nd Edition, 1999, Prentice-Hall.

Mathworks Home Page: www.mathworks.com