Introduction 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 ( ), Parentheses Enclose arguments of functions Enclose subscripts of vectors and matrices Indicate precedence in arithmetic expressions

Basic Matlab Review Plotting functions plot(), stem()  1-dimensional graphing mesh(), 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 window Ex: [audio_input, pathname] = uigetfile('*.wav', 'Please select a wav- file');

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

questdlg() Asks question – Yes-No-Cancel by default Ex: 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 Numbers For 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:

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 Reality EE 2303 Lab References: Oppenheim, Schafer. Discrete-Time Signal Processing. 2 nd Edition, 1999, Prentice-Hall. Mathworks Home Page: