MatLab Tutorial

What is it:

• Mathematics program for performing scientific and engineering calculations.
• Excellent tool for doing matrix manipulations and linear algebra.
• For more info, check out MIT's online help

Basics:

Help

• help topic: gives help on specified topic
• lookfor string: keyword search
• which function: locate functions and files

Line Editting

• CTRL-P Previous command
• CTRL-N Next command
• CTRL-A Beginning of command line
• CTRL-E End of command line
• CTRL-F Forward one character
• CTRL-B Back one character
• CTRL-K Delete line from cursor to end
• CTRL-D Delete next character
• CTRL-C Stop current command

Memory Management

• who list variables
• whos list variables and size
• clear varname removes variables, no arguments removes all variables.
• save foo saves to foo.mat, default is matlab.mat
• load foo retrieves foo.mat
• pack garbage collection
• diary save text of matlab session

Constants

• pi
• i,j
• eps
• Inf
• NaN

Matrix Manipulations

• A=[1 2 3; 4 5 6]
• A=[1 2 3
  4 5 6]
• t=[1:10]
• t=[1:0.1:10]
• A(1,:) selects first row
• A(:,1) selects first column
• A(:) makes A into a column vector
• size(A) matrix dimensions
• zeros(M,N) MxN matrix of zeros
• ones(M,N) MxN maxtrix of ones
• eye(M,N) MxN identity matrix

Matrix Operations

• +-*/\
• x=A\b => Ax=b
  x=b/A => xA=b
• ' transpose
• ^ power
• . element by element operations

Logical Relations

• <> <= >= == ~= & | ~(NOT)
• find returns indices of non zero elements
• any true if any element of a column vector is true
• all returns row vector of 1's and 0's indicating true or false over column of array

Vector Operations

• Operates columnwise
• mean, sum, prod, max, min
• diff first difference

Math

• sin,cos, exp, log
• abs, angle
• log, log10

Plotting

• plot(t,x) i.e. t=[0:800]; x=cos(2*pi.*t*(200)/8000;
• stem
• hold freeze/unfreeze
• title
• xlabel
• ylabel
• axis
• clf
• figure
• close
• subplot
• legend(linetype, 'string', linetype2, 'string2')
• ginput(Npoints)
• gtext('string')
• text(x,y,'string')
• set(gca)
• set(gcf)
• orientportrait, landscape, tall
• print

Programming

Flow Control

• for i=1:n (something) end
• if (bool) (something) elseif (something) end
• nargin number of input arguments
• nargout number of output arguments

Functions

function z=fcn(x,y)
%comment

z=x+y;

Efficiency

• tic;toc
• tic;foo;toc
• flops
• flops(0);foo;flops

Inefficient:

function y=cclip(x,limit)
% clips

y=x;
for i=1:length(y)

	if (abs(y(i))<limit)
		y(i)=0.0;
	end
end


Efficient:

function y=cclip2(x,limit)
% clips

y=x;
z=find(abs(y)<limit);
y(z)=zeros(size(z));

Signal Processing Functions

• filter(b,a,x) startup transients
• filtfilt(b,a,x) zero phase distortion, doubles filter length
• fftfilt(b,x) similar to filter except uses fft, good for short filter lengths and long signals.
• fft computes fft
• freqz(b, a, N, Fs) z transform digital filter frequency response
• fir1(L, Wp, window) window based FIR design