Hello everyone,

for my Master's thesis, I am trying to build a gravity model following the approach proposed in New nonlinear estimators of the gravity equation. In the article, the authors employ three estimators: a generalized nonlinear least squares estimator, and standard and generalized versions of the nonlinear Heckman two-step approach (using Matlab). I have searched whether Stata also provides commands for these estimators but I could, unfortunately, find nothing. Does someone know if it's possible to replicate these three estimators also in Stata?
Thanks a lot in advance to whoever is willing to help