# corNatural

##### General correlation in natural parameterization

This function is a constructor for the `corNatural`

class,
representing a general correlation structure in the ``natural''
parameterization, which is described under `pdNatural`

.
Objects created using this constructor must later be
initialized using the appropriate `Initialize`

method.

- Keywords
- models

##### Usage

`corNatural(value, form, fixed)`

##### Arguments

- value
an optional vector with the parameter values. Default is

`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).- form
a one sided formula of the form

`~ t`

, or`~ t | g`

, specifying a time covariate`t`

and, optionally, a grouping factor`g`

. A covariate for this correlation structure must be integer valued. 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.- fixed
an optional logical value indicating whether the coefficients should be allowed to vary in the optimization, or kept fixed at their initial value. Defaults to

`FALSE`

, in which case the coefficients are allowed to vary.

##### Value

an object of class `corNatural`

representing a general correlation
structure.

##### See Also

##### Examples

```
# NOT RUN {
## covariate is observation order and grouping factor is Subject
cs1 <- corNatural(form = ~ 1 | Subject)
# }
```

*Documentation reproduced from package nlme, version 3.1-145, License: GPL (>= 2) | file LICENCE*