corNatural {nlme} | R Documentation |

## General correlation in natural parameterization

### Description

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.

### 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.

### Author(s)

Jose Pinheiro Jose.Pinheiro@pharma.novartis.com and Douglas Bates bates@stat.wisc.edu

### See Also

`Initialize.corNatural`

, `pdNatural`

### Examples

## covariate is observation order and grouping factor is Subject
cs1 <- corNatural(form = ~ 1 | Subject)

[Package

*nlme* version 3.1-66

Index]