求平均值为什么一直找不到mean和average函数呢？代码：

. gen Markdown=average(markup,)if (markup ownership!=1)
unknown function average()
r(133);

. do "C:\Users\CHENGY~1\AppData\Local\Temp\STD29ac_000000.tmp"

. gen Markdown=mean(markup,)if (markup ownership!=1)
unknown function mean()
r(133);