[R] how to use nlme package to analysis mixed effect model

[PO SU]

Dear experts,
   i want to use nlme or plm to analysis mixed effect model, my data has the format :


  city  year  area    y   x   
   1    2010   A     1.2   2
   1    2011   A     3    3
    2   2010   A     5    4
    2   2011   A    2.1   1.8    3  2010  B      1.7    2
      ........


I want to know does y has relationsheep with x? how to use nlme or plm to do the  task?  the two packages seems does not have viggnette to guide me ? Does anyone happen to know ?


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PO SU
mail: desolator88 at 163.com 
Majored in Statistics from SJTU