看到很多文献里lme中的参数设置：random = ~1|分组变量

看了帮助，还是不理解~1是怎么解释
help里写的是：
optionally, any of the following: (i) a one-sided formula of the form ~x1
+...+xn | g1/.../gm, with x1+...+xn specifying the model for the random effects
and g1/.../gm the grouping structure (m may be equal to 1, in which case
no / is required).

括号里的话没看懂，是不是就是解释~1的意思？