clear

a1 = [1 2 3];
a2 = [4, 9, 10];

% create 3x2 matrix by joining columns
% two equivalent ways:
A = [a1.', a2.'];
A = horzcat(a1.', a2.');
A = cat(2, a1.', a2.'); % 2 selects the dimension that varies
                        % which is the dimension along which it concatenates
                        % 2 == column

% create a 2x3 matrix by joining rows
B = [a1; a2];
B = vertcat(a1, a2);
B = cat(1, a1, a2); % columns stay the same

% note:
assert(all(horzcat(a1, a2) == [1 2 3 4 9 10])); % not as above!

% also, comparision of row and column vectors gives non obvious result:
assert(all(a1 == a2.' == false(3), 'all'));

% ranges
assert(all(1:3 == [1 2 3]));
assert(all((1:3).' == [1 2 3]'));

% non integer ranges
% default step is 1
assert(all(1.5:3.5 == [1.5 2.5 3.5]));
% different step: note that 10 is included
assert(all(1 : 3 : 10 == [1 4 7 10]));
assert(all(1.3 : 2.2 : 5 == [1.3 3.5]));

C = [A [2 9 8].'];

% select one element
assert(C(2, 1) == 2);
% select element 1 and 3 on the second row
assert(all(C(2, [1 3]) == [2 9]));
% select element 1 and 3 on the first column
% note that the resulting entries are in a column vector
assert(all(C([1 3], 1) == [1 3].'));

% select the whole third row: progressively smarter
assert(all(C(3, [1, 2, 3]) == [3 10 8]));
assert(all(C(3, 1:3) == [3 10 8]));
assert(all(C(3, :) == [3 10 8]));

assert(all(C(:, :) == C, 'all'));

% select the whole second column
assert(all(C(:, 2) == [4 9 10].'));

% select the first and the third column, joining them
assert(all(C(:, [1 3]) == [1 2 3; 2 9 8].', 'all'));


% todo: linear indexing and logical indexing
%       sub2ind ind2sub
assert(all(A(:) == [1 2 3 4 9 10].'));

% remove elements from an array
D = [1, 3, 6, 2, 3, 1];
D(D == 3) = []; % remove all threes
assert(isequal(D, [1, 6, 2, 1]));