Fixed Variance Function

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.

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.

Author

José Pinheiro and Douglas Bates bates@stat.wisc.edu

See also

varClasses, varWeights.varFunc, varFunc

Examples

vf1 <- varFixed(~age)