st: nl command with restriction

["Rodolfo Coelho Prates" <rcprates@esalq.usp.br>]

Dear all!

I estimated a Cobb-Douglas function with additive error (nl command), the
coeficients are negative and the sum are larger than one, in some cases. 
I need that the coeficients are larger than zero and the sum of the
coeficients are equal to one. How can I estimate the function with
restriction in Stata?

Thanks,

Rodolfo

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