matlab tutorial

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Introducing Matlab (adapted from http://www.cns.nyu.edu/~eero and% http://www.cs.dartmouth.edu/~farid/teaching/cs88/matlab.intro.html)% via http://www-cse.ucsd.edu/%7Esjb/classes/matlab/matlab.intro.html%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% (1) Help and basics% The symbol "%" is used in front of a comment.% To get help type "help" (will give list of help topics) or "help topic"% If you don't know the exact name of the topic or command you are looking for,% type "lookfor keyword" (e.g., "lookfor regression")% When writing a long matlab statement that exceeds a single row use ...% to continue statement to next row.% When using the command line, a ";" at the end means matlab will not% display the result. If ";" is omitted then matlab will display result.% Use the up-arrow to recall commands without retyping them (and down% arrow to go forward in commands).  % Other commands borrowed from emacs and/or tcsh:% C-a moves to beginning of line (C-e for end), C-f moves forward a% character (C-b moves back), C-d deletes a character, C-k deletes % the line to the right of the cursor, C-p goes back through the% command history and C-n goes forward (equivalent to up and down arrows),% tab command completion.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% (2) Objects in matlab -- the basic objects in matlab are scalars,% vectors, and matrices...N= 5% a scalarv = [1 0 0]% a row vectorv = [1;2;3]% a column vectorv = v'% transpose a vector (row to column or column to row)v= [1:.5:3]% a vector in a specified range: v= pi*[-4:4]/4% [start:end] or [start:stepsize:end]v= []% empty vectorm = [1 2 3; 4 5 6]% a matrix: 1ST parameter is ROWS%     2ND parameter is COLS m= zeros(2,3)   % a matrix of zerosv= ones(1,3)  % a matrix of onesm= eye(3)% identity matrixv= rand(3,1)% random matrix with values in [0,1] (see also randn)load matrix_data % read data from a file:% create a file 'matrix_data' containing:% 2     3     4% 5     6     7% 1     2     3matrix_datav= [1 2 3];% access a vector elementv(3)%vector(number) % Index starts from 1m = [1 2 3; 4 5 6]m(1,3)% access a matrix element% matrix(rownumber, columnnumber)m(2,:)    % access a matrix row (2nd row)m(:,1)    % access a matrix column (1st row)size(m)% size of a matrixsize(m,1)  % number rowssize(m,2)  % number of columnsm1= zeros(size(m))% create a new matrix with size of mwho% list of variableswhos% list/size/type of variables%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% (3) Simple operations on vectors and matrices%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% (A) Pointwise (element by element) Operations:% addition of vectors/matrices and multiplication by a scalar% are done "element by element"a= [1 2 3 4];% vector2 * a % scalar multiplicationa / 4% scalar multiplicationb= [5 6 7 8];% vectora + b% pointwise vector additiona - b% pointwise vector additiona .^ 2% pointise vector squaring (note .)a .* b% pointwise vector multiply (note .)a ./ b% pointwise vector divide (note .)log( [1 2 3 4] )% pointwise arithmetic operationround( [1.5 2; 2.2 3.1] )% pointwise arithmetic operation%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% (B) Vector Operations (no for loops needed)% Built-in matlab functions operate on vectors, if a matrix is given,% then the function operates on each column of the matrixa= [1 4 6 3]% vectorsum(a)% sum of vector elementsmean(a)% mean of vector elementsvar(a)% variancestd(a)% standard deviationmax(a)% maximuma = [1 2 3; 4 5 6]% matrixa(:)                 % vectorized version of the matrixmean(a)                      % mean of each columnmax(a)                       % max of each column    max(max(a))     % to obtain max of matrix max(a(:))     % or...%%%%%%%%%%%%%%%%%%%%%%%%% (C) Matrix Operations:[1 2 3] * [4 5 6]'  % row vector 1x3 times column vector 3x1                     % results in single number, also                   % known as dot product or inner product[1 2 3]' * [4 5 6]  % column vector 3x1 times row vector 1x3                    % results in 3x3 matrix, also                    % known as outer producta= rand(3,2)% 3x2 matrixb= rand(2,4)% 2x4 matrixc= a * b% 3x4 matrixa= [1 2; 3 4; 5 6]% 3 x 2 matrixb= [5 6 7];% 1 x 3 vectorb * a% matrix multiplya' * b'% matrix multiply%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%(4) Saving your worksave mysession      % creates mysession.mat with all variablessave mysession a b  % save only variables a and bclear all% clear all variablesclear a b           % clear variables a and bload mysession% load sessionab%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%(5) Relations and control statements% Example: given a vector v, create a new vector with values equal to% v if they are greater than 0, and equal to 0 if they less than or% equal to 0.v= [3 5 -2 5 -1 0]% 1: FOR LOOPSu = zeros( size(v) );% initializefor i = 1:size(v,2)% size(v,2) is the number of columnsif( v(i) > 0 )u(i) = v(i); endenduv= [3 5 -2 5 -1 0]% 2: NO FOR LOOPSu2= zeros( size(v) );% initializeind= find( v>0 )% index into >0 elements u2(ind)= v( ind )%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%(6) Creating functions using m-files:% Functions in matlab are written in m-files. Create a file called % 'thres.m' In this file put the following 4 lines:function res = thres( v )u= zeros( size(v) );% initializeind= find( v>0 )% index into >0 elements u(ind)= v( ind )v= [3 5 -2 5 -1 0]thres( v )% call from command line%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%(7) Plotting x= [0 1 2 3 4];% basic plottingplot( x );plot( x, 2*x );axis( [0 8 0 8] );x = pi*[-24:24]/24;plot( x, sin(x) );xlabel( 'radians' );ylabel( 'sin value' );title( 'dummy' );gtext( 'put cursor where you want text and press mouse' );figure;% multiple functions in separate graphssubplot( 1,2,1 );plot( x, sin(x) );axis square;subplot( 1,2,2 );plot( x, 2.*cos(x) );axis square;figure;% multiple functions in single graphplot( x,sin(x) );hold on;              % hold on tells matlab to write on top plot (x, 2.*cos(x), '--' );% of the current plotlegend( 'sin', 'cos' );hold off;figure;% matrices as imagesm = rand(64,64);imagesc(m)colormap gray;axis imageaxis off;%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%(8) Working with the Images and the Matlab Image Processing Toolbox[I,map]=imread('trees.tif');            % use as it is, Matlab has pre-stored imagesfigureimshow(I,map)                           % display it as indexed image w/colormapI2=ind2gray(I,map);                     % convert it to grayscalefigureimagesc(I2,[0 1])                       % scale data to use full colormap                                        %  for values between 0 and 1colormap('gray')                        % use gray colormapaxis('image')                           % make displayed aspect ratio proportional                                        %  to image dimensions I=imread('football.jpg');               % read a JPEG image into 3D arrayfigureimshow(I)rect=getrect;                           % select rectangleI2=imcrop(I,rect);                      % cropI2=rgb2gray(I2);                        % convert cropped image to grayscaleimagesc(I2)                             % scale data to use full colormap                                        %  between min and max values in I2colormap('gray')colorbar                                % turn on color barimpixelinfo                             % display pixel values interactivelytruesize                                % display at resolution of one screen pixel                                        %  per image pixeltruesize(2*size(I2))                    % display at resolution of two screen pixels                                        %  per image pixelI3=imresize(I2,0.5,'bil');              % resize by 50% using bilinear                                         %  interpolationI3=imrotate(I2,45,'bil','crop');        % rotate 45 degrees and crop to                                        %  original sizeI3=double(I2);                          % convert from uint8 to double, to allow                                        %  math operationsimagesc(I3.^2)                          % display squared image (pixel-wise)imagesc(log(I3))                        % display log of image%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%