mimics gauss function xpnd
mat=xpnd1(v,nr)
v = a (nr x 1) vector
nr = # of rows of the original matrix
mat = the original -vectorized by vech_gauss- matrix
v=1:5;mat=v'*v;vh=vech_gauss(mat);matr=xpnd1(vh,5);matr-mat // mat is a (5 x 5) symmetric matrix. vh is the corresponding (15 x 1) vectorisation. You can check that mat and matr are the same.