varClasses: Variance Function Classes

In nlme: Linear and Nonlinear Mixed Effects Models

Variance Function Classes

Description

Standard classes of variance function structures (varFunc) available in the nlme package. 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.

Value

Available standard classes:

varExp	exponential of a variance covariate.
varPower	power of a variance covariate.
varConstPower	constant plus power of a variance covariate.
varConstProp	constant plus proportion 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.

Note

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.

Author(s)

José Pinheiro and Douglas Bates [e-mail]

References

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

See Also

varComb, varConstPower, varConstProp, varExp, varFixed, varIdent, varPower, summary.varFunc

nlme documentation built on Nov. 27, 2023, 5:09 p.m.