Variance Function Classes

DESCRIPTION:

Standard classes of variance function ( varFunc) structures available in the nlme3 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.

VALUE:

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

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 the varPower class.

SEE ALSO:

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