st: boundary constraints within nl

[Marc Keuschnigg <Marc.Keuschnigg@soziologie.uni-muenchen.de>]

Hey,

I am estimating non linear least squares models (nl) using equations 
like: nl (y =  ({a}+{b}* x) * (1-x)).
My question is, how do I impose parameter restrictions like a >=0 and b 
>=0?
I could log-transform the parameters, but I don't know how to do it 
technically within the nl command.

Thanks for helping,
Marc



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