%% Programming Languages Matlab 3101 - Class 3
% 3/26/08, Instructor: Blake Shaw

%% Notes: HW1 grades, Quiz,
% HW 1, avg is 82.5, std deviation is 14, quiz is next week, it will be the
% second half of class, 1 hour, closed book, closed computer, closed
% everything.

%% Review
% Loops, and Control flow: if, while, for, try/catch.  Displaying text with
% formatting.  More plotting: spy, imagesc.  

%% Today: focus on data structures
% matrices (including numbers, and lists), strings, cells, saving and
% loading



%% Numbers, Lists, and Matrices
% show some examples with [], cat, indexing, transpose, flip, rot90,
% reshape, flattening with (:)

%%

a = 34;

A = [4, 5; 6, 8; 10, 15]

B = [7, 8; 10, 12]

C = [A; B; [9, 8]]


C = [A', B]

D = [A(1:2, 1:2), B]

%%
A = round(10*rand(3, 2))

B = round(10*rand(3, 2))

C = round(10*rand(3, 2))

D = cat(3, A, B, C);

size(D)

%% 

A = round(20*rand(3, 3));

fliplr(A)
flipud(A)

A
rot90(A)

sum(sum(sum(D)))
sum(D(:))


flatD = D(:);

reshape(flatD, 3, 6)

%% Creating special matrices
% zeroes, ones, eye, diag, linspace, :, rand, randn

A = zeros(3, 2, 4)
A = ones(3, 3)

A = eye(3, 3)


A = diag(eye(3, 3))

A = diag([2, 3, 5, 7])

b = linspace(-pi, pi, 1000);

length(b) 
plot(b, sin(b))

a = 6:0.2:9;

length(a)

%%
a = rand(10000, 1);
b = randn(10000, 1);

hist(a)
hist(b)

%% Matrices can be high-dimensional
% squeeze, shiftdim

D = floor(10*rand(3, 2, 3))

D2 = sum(D, 2)

size(D2)

D3 = squeeze(D2)


size(D3)

%%

D

size(D)

D4 = shiftdim(D, 3)

size(D4)

%% circshift

A = floor(10*rand(5, 5))

%%
A

circshift(A, 1)

circshift(A, [1, 1])



%% Matrices can be sparse
% sparse, nnz, nonzeros, sprand

N = 10^3;
A = zeros(N, N);

size(A)

%%
N = 10^5;
B = sparse(N, N);

size(B)

%%
B(1, 5) = 9;
B(4, 9) = 12;

B = B .^ 2;

B(1, 5)
%%
nnz(B)

nonzeros(B)



C = sprand(N, N, 0.0005);

%%
nnz(C)
imagesc(C(1:100, 1:100)); axis image;



%% Creating indexes
% :, randperm, sub2ind, ind2sub

X = rand(100,1);
N = length(X);

i = randperm(N);
X(i(1:10))


[i, j] = ind2sub([5, 5], 14)


%% Avoiding loops
% repmat, find, circshift, relational operators, sort, permute


a = rand(10, 10);

%%
[i, j] = find(a < 0.5)


[i, j]


%%
a = [1, 2, 3]
a([2, 1, 3])


%%
X = rand(100, 2);
p = rand(1, 2);

%%
figure(1); clf;
hold on;
scatter(X(:, 1), X(:, 2))
scatter(p(1, 1), p(1, 2), 'r+')
hold off;

%%



dists = sum((X - repmat(p, 100, 1)).^2, 2);
i = find(dists < 0.01)

[C, I] = min(dists)



%% Strings
% declaring, concatenating, indexing, converting, strfind, strtok

a = 'hello';

length(a)

b = [a, ' blake'];


strfind(b, 'll')

strfind(b, 'afdas')


%c = ['string1'; 'this is string 2'; 'hi']





%% basic types: double, char unit8
char(double(b) + 1)


b(5)

b(2:5)


%% Cells
% declaring, concatenating


A = cell(4, 1);

A{1} = 'this is a string';

A{2} = rand(10, 10);

A{3} = 'this is another string';

A{4} = cell(2, 2);


B = cell(2, 2)

C = cell(2, 2)

D = {B, C}

D = {rand(10), 10, 'hello'}

D = [B C]

%% Saving and Loading variables
% who, whos, clear, save, load

whos

save results.mat

clear

whos

whos -file results.mat

load results.mat

%% User Input
% input, str2num


s = input('what is the temp today?\n', 's');

%%

str2num(s) + 1

%% About HW3
% Talk about rot13 encoding, and the caesar cipher


%% Quiz review

%{
Class Notes 1:3

Working with matrices:
http://www.mathworks.com/access/helpdesk/help/techdoc/index.html?/access/helpdesk/help/techdoc/math/f4-988203.html

Basic Flow Control:
http://www.mathworks.com/access/helpdesk/help/techdoc/index.html?/access/helpdesk/help/techdoc/learn_matlab/f4-1931.html

%}