In a scientific paper I am currently working with, a definition of $Col$ and $Diag$ operator is introduced:
We use the operator $Col_{k\in K}(x_k)$ which stacks up its vector (or matrix) arguments $x_k$ for all $k$ in the index set $K$ into a vector (or matrix respectively), and the operator $Diag_{k\in K}(x_k)$ which builds a (block) diagonal matrix out of its scalar or square matrix arguments $x_k$ for all $k$ in $K$.
Probably due to the fact, that English is not my mother tongue, I do not understand, how the described operators are used on vectors and matrices.
Could you please provide an example of usage of these operators on a vector and a matrix and what is the expected result?