st: cholesky decomposition

[Narasimhan Sowmyanarayanan <narasimhan.sowmyanarayanan@gmail.com>]

I am trying to do the cholesky decomposition of the vce matrix in
stata and am finding that it says its not positive definite. After
running the regression I specify

reg x y z
matrix v = e(vce)
matrix c = cholesky(v)

I get the following error:

"cholesky(): matrix has missing values"

I checked the help in stata and it says that I can use _cholesky()
option. But if I try that then I get the following


. matrix c = _cholesky(v)
unknown function _cholesky()

I was wondering if I am doing something wrong ? Some insights will be
highly appreciated from the knowledgeable members.

Best
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/