st:coefficients nonlinear constraint

[Juan Pablo Maícas <jpmaicas@unizar.es>]

Hello Statalisters,
I need to estimate a model of simultaneous equations that presents 
coefficients nonlinear constraint. I have the following model 
Y1=X1*b1+X2*b3, Y2=X2*b2. I want to estimate these two equations by 3sls 
subject to constraint that b1=b2/b3.
Please, let me know how to do this in Stata.
Thank you very much and I appreciate your help
Juan Pablo

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