Practice

clear all
close all

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
add = 0;
N=1e7;

tic % timer
for i = 1:1:N ;
    add = add +i;
end
toc

add

tic
sum(1:1:N)
toc

tic
v = 1:1:N;
addv = ones(1,N) * v'
toc
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

a = magic(3)
sum(sum(a,1),3)

%clc --> clear screen

a = magic(3)
b = eye(3)

a*b
a.*b    % multiplication of non matrix
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
a = magic(2)
a'
fliplr(a)
flipud(a)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
a=-3
abs(a) % absolute number
b=4
c=a+j*b
abs(c) % in complex number is the length
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
zeros(2,3)
a=[1 1;1 2]
inv_a = inv(a)
a*inv_a
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
a = magic(3)
a(:,2)
a(3,:)
a(2,2)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
load durer
image(X)
imshow(X/255) %X/256 cause the value is too big
whos

dither_m = [0.1 0.5;0.7 0.3]

for x=1:size(X,2)
    for y=1:size(X,1)
        i=mod(x,size(dither_m,2))+1;
        j=mod(y,size(dither_m,1))+1;
        Y(x,y)=X(x,y)>dither_m(i,j);
    end
end

X=X(:,1:508)
image(X)
image(Y)