%% Programming Languages Matlab 3101 - Class 2
% 3/12/08, Instructor: Blake Shaw


%% Review
% can make variables, numbers, lists, matrices, can index them in
% interesting ways, and apply mathematical functions to them

% working with variables
3+4

a = 5
b = 7;

x = a^b


%working with lists
list1 = 3:5:94

list1 .^ 2

[list1(1:5).^2, list1(6:end).^3]


% basic eigenvalue decomposition
A = rand(10, 10);

[v, d] = eig(A);


% lets factor and recompose a large number
x = factor(345345435);

prod(x)



%% control flow in scripts
% if, for, while, try, catch
a = 3;
b=4;

a > b
(a<b) + (a<b)

a == b

a ~= b

a >= b


%% if statements
% if/else, booleans with ands and ors, and other relational operators

A = floor(10*rand(2, 2));
B = floor(10*rand(2, 2));

if (sum(A, 1) > 3)
    X = 4;
else
    X = 5;
end


if (a < 100) && (b < 5)
    X = 1000
else
    X = 0
end

if (a < 100) || (b < 2)
    X = 1000
else
    X = 0
end

if (a<100 && (b-10) ~= -3) || a == 6
   X = 1000 
end
    
if X > 0 && eig(X) <= -1
    X = 1000
end



%% while loops
% similar to if statements... careful about infinite loops, contorl-c to
% exit

x = 100;

while x > 50
    x = x - log(x)
end

% this is an infinite loop -- it runs forever!!!

%{
% these are also multiline comments!
while 1
   x = x+1;
end
%}


%% for loops
% count up, count down, and by different increments

1:1

3:36

3:2:36

45:-3:0

for i=1:5
   i
   X = rand(i, i); 
   sum(sum(X))
   max(max(X))
end

% some stuff does not need to be looped
for i=1:2:8
    i^2
end

(1:2:8).^2

indices = ceil(100*rand(10, 1))';

X = (1:100).^2;

runningTotal = 0;
for i=indices
    i
    runningTotal = runningTotal + X(i);
end

runningTotal

% write without a loop?

runningTotal2 = sum(X(indices))


N=10;
A = rand(N, N);

for i=1:N
    for j=1:N
        A(i, j) = A(i, j)^2 + sin(pi * (i/N));
    end
end


for i=1:30
   if i < 15
      x = 5; 
   end
end

%% try and catch
% good for catching and dealing with errors




for i=1:10
   A = rand(10, 3);
   B = rand(5, ceil(3*rand())); 
   
   try 
       result = A * B';
   catch
       disp('Loop caused an error');
       disp(sprintf('Size of B: %f', size(B, 2)));
   end
   
end

result


%% disp and sprintf, helpful printing in loops
% like c, %g, %d, %s

X = 5;

disp(X)

X = [1, 34, 54, 6]
disp(X)

disp('this is a string');

X = 5;

disp(sprintf('X is equal to %d and some number is %d', X, 10));


str = 'blake';
x = length(str);
disp(sprintf('"%s" has %d characters', str, x))



x = [1, 234, 3,4, 34];
disp(sprintf('x is equal to %d\n', x))


pi
disp(sprintf('%1.100g', pi))

%% formatting ouput with the format command
% short, long


%% more practice with creating matrices
% zeroes, ones, eye, diag, linspace, :


%% more practice with creating indexes
% :, randperm, sub2ind, ind2sub


%% more plotting
% using imagesc to plot a matrix, or spy, title plots, set axes, change colormap,
% specify which figure

A = rand(10, 10);
A(2, :) = 0;
imagesc(A)
colormap('gray');
title('my random matrix');



A(find(A > 0.2)) = 0;

spy(A)

%% avoiding loops
% repmat, find

N = 10;
x = 1:N;

repmat(x, N, 1)