gnlsStruct.RdA generalized nonlinear least squares structure is a list of model
components representing different sets of parameters in the nonlinear
model. A gnlsStruct may contain corStruct and
varFunc objects. NULL arguments are not included in the
gnlsStruct list.
gnlsStruct(corStruct, varStruct)a list of model variance-covariance components determining the parameters to be estimated for the associated nonlinear model.