各位大神，我在用rqpd包计算面板分位数，固定效应模型设定中，s 变量难道我了，下面是help文件中的部分：  请各位大神对s 变量的选取给以指导   

rqpd(formula, panel = panel(), data =parent.frame(),

   na.action, subset, contrasts = NULL, control = NULL, ...)

formula

            

A method-specific formula  for the model employing the conventions of theFormula package,  which has the additional operator "|". "rqpd"-formulas  are specified as:

  

   

FE:

             

y ~ x1 + x2 + ... | s

   

   

CRE:

             

y ~ x1 + x2 + ... | s | z1 + z2 + ...

   

  

The portion of the formulas  before the (first) vertical bar is specified like the conventional lm or rq function formulas.

  

The factor variable s specifies the structure of the panel, and in  the FE model it represents the "fixed effects". This is typically  an id column.

  

The last part of the CRE  formula is a specification of the variables in the CRE component. These are  possibly endogenous variables (in the sense that they are affected by the  fixed effects) and must be time-varying. Note that there are two vertical  bars.