st: missing output in ml

[Ian Breunig <ianbreunig@gmail.com>]

Statlist,

After running ml on a system of equations with a user written
likelihood function, I find that sometimes the results show missing
values ('.') for the standard errors and related results on some of
the estimated '_cons', and sometimes for  other constants being
estimated in the model.  The e(v) matrix shows that the variance
matrix has a zero across the row for this parameter. The coefficient
itself is estimated. Can anyone tell me what this means?  What is
going wrong or what does this imply?  (The same results occur when I
use pweights and svyset with pweights specified).

I've searched through the Gould et al. book, and searched the web
already but couldn't find an answer.

 Thanks.

Ian Breunig
*
*   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/