/*
  user-level function: estimate the model and print out
  the results
*/
function void zip(series y, list X)
    matrix coef_stde = zip_estimate(y, X)
    printf "\nZero-inflated Poisson model:\n"
    string parnames = "alpha,"
    string parnames += varname(X)
    modprint coef_stde parnames
end function