这是一些作者给的的程序，可以出来，我试过了。改第一个命令就行。
* Estimate the model
poisson trade lypex lypim lyex lyim  ldist border comlang colony landl_ex landl_im lremot_ex lremot_im comfrt_wto open_wto, robust

* Get fitted values of trade
predict fitted

* Compute correlation between trade and fitted values
qui cor fitted trade

* Display R2 computed as the square of the correlation between trade and fitted values
di as txt " R-squared   "  (`r(rho)')^2