st: triangular matrices

In response to Brendan's desire to generate a Stata matrix from its lower triangle: if this is meant to be a 4x4 matrix, what is on the diagonal? I have put zeroes on the diagonal:

clear
input v1 v2 v3
1 1 0
1 2 12
1 3 13
1 4 14
2 2 0
2 3 23
2 4 24
3 3 0
3 4 34
4 4 0
end
mkmat v3,mat(a)
mata: st_matrix("b",invvech(st_matrix("a")))
mat list b

Kit Baum, Boston College Economics
http://ideas.repec.org/e/pba1.html
An Introduction to Modern Econometrics Using Stata:
http://www.stata-press.com/books/imeus.html

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