How to run gravity model PPML with constrained parameter on GDP?

[Bushra Faizi]

Dear professors,
I have bilateral trade data for 119 countries and the year 2014. I want to run the gravity model, PPML I have to run separate regression for each sector. The GDP of the importer countries in the model is constrained to be 0.8. What are the stata commands to run the gravity model with such constraint?
Thank you.

[Bushra Faizi]

REMINDER please

[Joao Santos Silva]

The commands that implement PPML have an "offset" option that allows you to do that.