st: I have a problem with xtgls hetero and serial correlation

[Rodrigo L�pez <rodrilopez88@hotmail.com>]

Hy Statalist

I have 13 observation and 15 panels unit. When I run xtgls and xtreg, fe I 
have problem becuase the Stata told me that correlation matrix is singular 
and It is not possible do the test. How can I do for test serial correlation 
in xtgls and extreg; fe?.

My best regards
Rodrigo Lopez

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