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 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)

José Pinheiro and Douglas Bates [email protected]

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)