各位大佬，本人在尝试用stata的gtfpch命令测算上市公司绿色全要素生产率。在跑下面这段代码时候，会报错。但是检查了数据集里面是有gk这个变量的。求帮忙看看是哪里有问题。use sample, clear
qui su i
loc max = r(max)
forv i = 1/`max'{
use d3, clear
keep if i == `i'
gtfpch lnK lnL lnE = lnY : lnSO2_ lnWater_ lnDust_, ///
dmu(Stkcd) gx(gk gl ge) gy(gy) gb(gb1 gb2 gb3) ///
global sav(GTFP_`i'.dta, replace)
use GTFP_`i',clear
split Pdwise,p(~)
drop Pdwise1
ren Pdwise2 year
destring year, replace
ren (TFPCH TECH TECCH) (GTFP GTEC GTC)
save GTFP_merge_`i',replace
}


显示

variable gk not found
(error in option gx())
r(111);