title: Nonlinear model (with country and time fixed effects)
body: <p><a href="https://i.stack.imgur.com/Au4Mo.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Au4Mo.png" alt="enter image description here"></a></p>
  
  <p>I try to estimate the above nonlinear model by Stata. Unfortunately, I am not comfortable with Stata. Can anyone help me about writing the above function in Stata?
  How can we write regional dummy, time fixed effect and country fixed effect in <code>nl</code> command in Stata?
  Is there a way to write the summation in the above equation in Stata? Alternatively, is it easier to estimate the equation for each individual region?</p>