* v = output vector containing stacked columns of x
DESCRIPTION
Mimics gauss function vech, that a creates a column vector by stacking columns of x on and below the diagonal. Note that the conventions are not the same as for grocer function vech.
EXAMPLE
v=1:5;mat=v'*v;vh=vech_gauss(mat)// mat is a (5 x 5) symmetric matrix. vh is the corresponding (15 x 1) vectorisation.