OptionalomegaThe weights omega_i of the meat instead of the type's: an array of one value per row of non-zero weight (or one per
row used, those of weight 0 then left out), or a function (res, hat, df) => omega of the residual factors, the
hat values and n - k.
OptionalsandwichReturn the sandwich (default true) or the meat only (false).
OptionaltypeThe estimator: "HC3" (default), "const", "HC0" (alias "HC"), "HC1", "HC2", "HC4", "HC4m" or
"HC5". Unambiguous abbreviations are accepted, as R's match.arg.
Options for vcovHC.