corSymm
class,
representing a general correlation structure. The internal
representation of this structure, in terms of unconstrained
parameters, uses the spherical parametrization defined in Pinheiro and
Bates (1996). Objects created using this constructor must be later
initialized using the appropriate
initialize
method.
corSymm(value, form, fixed)
numeric(0)
, which results in a vector of zeros of appropriate
dimension being assigned to the parameters when
object
is
initialized (corresponding to an identity correlation structure).
t
and, optionally, a grouping factor
g
. A covariate for
this correlation structure must consist of consecutive integers
starting at
1
. When a grouping
factor is present in
form
, 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. Defaults to `~ 1', which corresponds to using the order
of the observations in the data as a covariate, and no groups.
FALSE
, in which case
the coefficients are allowed to vary.
corSymm
representing a general correlation
structure.
Pinheiro, J.C. and Bates., D.M. (1996) "Unconstrained Parametrizations for Variance-Covariance Matrices", Statistics and Computing, 6, 289-296.
## covariate is observation order and grouping factor is Subject cs1 <- corSymm(form = ~ 1 | Subject)