varFixed {nlme} | R Documentation |

## Fixed Variance Function

### Description

This function is a constructor for the `varFixed`

class,
representing a variance function with fixed variances. Letting *v*
denote the variance covariate defined in `value`

, the variance
function *s2(v)* for this class is
*s2(v)=|v|*. The variance covariate *v* is
evaluated once at initialization and remains fixed thereafter. No
coefficients are required to represent this variance function.

### Usage

varFixed(value)

### Arguments

`value` |
a one-sided formula of the form `~ v` specifying a
variance covariate `v` . Grouping factors are ignored. |

### Value

a `varFixed`

object representing a fixed variance function
structure, also inheriting from class `varFunc`

.

### Author(s)

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

### References

Pinheiro, J.C., and Bates, D.M. (2000) "Mixed-Effects Models
in S and S-PLUS", Springer.

### See Also

`varClasses`

,
`varWeights.varFunc`

,
`varFunc`

### Examples

vf1 <- varFixed(~age)

[Package

*nlme* version 3.1-80

Index]