% Initialize
m = 5000;
n = 5000;
x = 3 * ones(m,1);
A = 0.001 * ones(m,n);
y = zeros(n,1);

% Loop
tic;
for i=1:m
    y(i) = 0;
    for j=1:n
        y(i) = y(i) + A(i,j) * x(j);
    end
end
toc;

% Efficient Way
tic;
y = A * x;
toc;

% Almost Efficient
tic;
for i=1:m
    y(i) = A(i,:) * x;
end
toc;

% Bad Way to Initialize
clear x;
clear y;
clear A;
tic;
for i=1:m
    x(i) = 3;
end
for i=1:m
    for j=1:n
        A(i,j) = 0.001;
    end
end
toc;