Multiple linear regression

Dear R-users,
I've a question regardiing multiple linear regression.
Is it possible to regress a function of the type
y=b0+b1*x1+b2*x2
constraining the partial derivatives dy/dx1 and dy/dx2 to be greater
than 0 ???

Thank you very much for any possible suggestion.
Best regards
Marco


--
Marco Pagani - PhD Student
Dipartimento di Scienze della Terra - Sezione Geofisica
Universita' degli Studi di Milano
c/o
CSGAQ - CNR
via Bassini, 15 - I-20133 Milano - Italia
tel: +39-02-23699455
fax: +39-02-26680987 / +39-02-2362946



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