Vectorization of Variance-Covariance Matrix: Column-Wise Order (Multidimensional Arrays)

Creates a column vector by stacking elements of x that are on and below the diagonal.

Creates a column vector by stacking elements of x that are on and below the diagonal; each column is placed into a matrix. It does this in column-wise order. Created because I could not get Mike Cliff's vech function to work on multidimensional arrays.