I wish I knew MATLAB had... kron

• The function kron creates the Kronecker (tensor) product of two arrays. Why on earth would this ever be useful?
• You can use it instead of repmat for certain tasks. Let's say you have an array 

  x = [1,3,5,7]

• What if you now wanted to triplicate each element, to get [1,1,1,3,3,3,5,5,5,7,7,7]? You might try repmat:

  y = repmat(x,3,1);   y=y(:);

• which simply creates three rows and then "flattens" the matrix to a vector. But using kron can be simpler:

  y = kron(x,[1 1 1])

• This replaces each element of y with y(i) * [1 1 1], giving the desired 9 elements.