%%% A script to illustrate some simple matlab concepts

%%% Creating and fiddling with matrices

disp('%% create a matrix of ones');
disp('%% x = ones(3,3)');

x = ones(3,3)

disp('%% create a matrix of random values');
disp('%% y = rand(3,3)');
y = rand(3,3)

disp('%% Add them');
disp('%% z = x + y');
z = x + y

disp('%% concatenate the rows');
disp('%% zz = [x,y]');
zz = [x,y]   %% a 3 by 6 matrix

disp('%% concatenate the columns');
disp('%% zz = [x;y]');
zz = [x;y]   %% a 6 by 3 matrix

disp('%% symmetrize y')
disp('%% w = y + y'' ');
w = y + y'   %%% here ' denotes transpose

disp('%% the first two rows of the first and 3rd columns');
disp('%% w = w(1:2,1,3)');
w = w(1:2,[1,3]) 

disp('%%  string it out as a vector');
disp('%% wv = w(:)       ');
wv = w(:)       

disp('%%  essentially dot product');
disp('%% normval = wv'' * wv   ');
normval = wv' * wv   

disp('%% same as the above');
disp('%% normval = dot(wv,wv)  ');
normval = dot(wv,wv)  

disp('%%  count the number of positive elements');
disp('%% sum(wv > 0)          ');
sum(wv > 0)          

disp('%%  set all the zero values to 1');
disp('%% wv(wv == 0) = 1      ');
wv(wv == 0) = 1      

disp('%%  divide each element of wv by the');
disp('%% corresponding element of the reversed string');
disp('%% wv = wv./wv(end:-1:1)  ');
wv = wv./wv(end:-1:1)  
 
disp('%% Create a string');
str = 'teststring'  

disp(['a test string is ','string'])  %% string concatenation
disp(sprintf('with length %d',length(str)))  %% formatting

%%% Some image things

disp('%%  read an image');
disp('%% im = imread(''peppers.png'');  ');
im = imread('peppers.png');  

disp('%% % should be uint8');
disp('%% class(im)   ');
class(im)   

disp('%% % convert to preferred doubles in range 0 to 1');
disp('%% im = double(im)/255;   ');
im = double(im)/255;   

disp('%% show it');
disp('%% imshow(im)  ');
imshow(im)  

disp('%% green band');
disp('%% gim = im(1:2:end,1:2:end,2);   ');

disp('%% red band');gim = im(1:4:end,1:4:end,2);   
disp('%% rim = im(1:4:end,1:4:end,1);   ');

disp('%% blue band');rim = im(1:4:end,1:4:end,1);   
disp('%% bim = im(1:4:end,1:4:end,3);   ');
bim = im(1:4:end,1:4:end,3);   

disp('%% show all the separate bands');
newim = [rim;gim;bim];
imshow(newim);
imwrite(newim,'newim.pgm','pgm');