varClasses {nlme}R Documentation

Variance Function Classes


Standard classes of variance function structures (varFunc) available in the nlme library. Covariates included in the variance function, denoted by variance covariates, may involve functions of the fitted model object, such as the fitted values and the residuals. Different coefficients may be assigned to the levels of a classification factor.


Available standard classes ():

varExp exponential of a variance covariate.
varPower power of a variance covariate.
varConstPower constant plus power of a variance covariate.
varIdent constant variance(s), generally used to allow different variances according to the levels of a classification factor.
varFixed fixed weights, determined by a variance covariate.
varComb combination of variance functions.


Users may define their own varFunc classes by specifying a constructor function and, at a minimum, methods for the functions coef, coef<-, and initialize. For examples of these functions, see the methods for class varPower.


Jose Pinheiro and Douglas Bates

See Also

varExp, varPower, varConstPower, varIdent, varFixed, varComb

[Package nlme version 3.1-57 Index]