This function is generic; method functions can be written to handle
  specific classes of objects. Classes which already have methods for
  this function include: "corSpatial", "corStruct",
  "pdCompSymm", "pdDiag", "pdIdent", "pdMat",
  and "pdSymm".
Dim(object, ...)will depend on the method function used; see the appropriate documentation.
any object for which dimensions can be extracted.
some methods for this generic function require additional arguments.
José Pinheiro and Douglas Bates bates@stat.wisc.edu
Dim.corSpatial,
  Dim.pdMat, Dim.corStruct