With much of the tribal region dominated by several Taliban factions, the government is turning to an old practice of striking agreements with local tribal militias, called lashkars,to handle security.

VOA: standard.2009.03.26

In fact, there are some very old books that show this as the average, the sum divided by two arithmetic mean, but the modern practice is to use the geometric mean.

事实上，一些很老的书籍上,平均的定义就是算数意义的，总的来说被分为两种算数意义，但现代我们多用几何意义。

麻省理工公开课 - 固态化学导论课程节选