st: Inequality constraints in single and multi-equation models

[Marcello Pagano <pagano@hsph.harvard.edu>]

Posted for Michael :

> Hello all,
>
> In the process of estimating an econometric cost function and associated
> share equations (using Stata 8.0), I have tried to estimate an equation
> with constraints that three of the parameters sum to one.  While these
> constraints held when estimating a single equation for the cost function
> with the -cnsreg- command, the estimates of the parameters (input
> shares) took on values less than zero and greater than one, which are
> not possible in practice.
>
> To compensate, I tried defining additional constraints that the three
> parameters take on values between zero and one, using syntax such as: 
> define constraint 7  0 < lnpl < 1. 
> I tried this twice, receiving error messages, "0 not found" and then "<
> not found".  I interpreted this as meaning either the syntax was
> incorrect or this type of constraint simply cannot be estimated using
> Stata.  I hope I am wrong.
>
> Any suggestions or clarifications as to 1)  Whether such constraints can
> be used in estimation with Stata and 2) if so, how they can be
> incorporated into an estimation process using -sureg- or, failing that,
> -cnsreg-, would be greatly appreciated.
>
> --Michael Iacono
>
>  
*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/