nlme (version 3.1-150)

varFixed: 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 ${\sigma }^2(v)$ for this class is ${\sigma }^2(v)=|v|$. 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.

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

# NOT RUN {
vf1 <- varFixed(~age)
# }