This function is a constructor for the
corStrat class,
representing a set of correlation structures corresponding to
different strata, defined by
strata. Different
corStruct
classes can be used for different strata. The number
of coefficients associated with this class is equal to the sum of the
number of coefficients of each
corStruct object it includes.
Objects created using this constructor must later be initialized
using the appropriate
initialize method.
USAGE:
corStrat(value, form, strata)
REQUIRED ARGUMENTS:
value
a
corStruct object, or a list of
corStruct
objects. If given as a single object, it is repeated for all strata.
strata
a one-sided formula specifying the stratification variable
for the different
corStruct objects represented by
object. Its right hand side must evaluate to a factor or an
integer.
OPTIONAL ARGUMENTS:
form
an optional one sided formula of the form `~ t', or
~ t | g, specifying a time covariate
t and, optionally, a
grouping factor
g. The same formula is used for all
corStruct represented in
object. When a grouping factor is
present, the correlation structure is assumed to apply only
to observations within the same grouping level; observations with
different grouping levels are assumed to be uncorrelated.
VALUE:
a
corStrat object representing a set of correlation structures
corresponding to different strata.