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Introduction to Matlab II

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

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Introduction to Matlab II

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  1. Introduction to Matlab II EE 2303 Lab

  2. 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

  3. 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

  4. Basic Matlab Review • Plotting functions • plot(), stem() 1-dimensional graphing • mesh(), imagesc() 2-dimensional visualization

  5. 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.

  6. Creating Arrays zeros(M,N) create M-by-N zeros matrix ones(M,N) create M-by-N ones matrix

  7. User Interface Commands • More user-friendly • Looks slicker • Principal UI commands • uigetfile() – retrieve files • questdlg() – input logical buttons • inputdlg()– input values

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

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

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

  11. guide • GUI Design Environment • Alter .fig files • Design self-contained gui’s

  12. Debug Mode • Used for scripts

  13. 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

  14. Discrete Fourier Transform • Used to find frequency response of digital signals • Discrete signal input  DFT  discrete frequency response • Matrix form of DFT:

  15. 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)')

  16. 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)')

  17. 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

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

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