

varClasses(nlme)                             R Documentation

_V_a_r_i_a_n_c_e _F_u_n_c_t_i_o_n _C_l_a_s_s_e_s

_D_e_s_c_r_i_p_t_i_o_n_:

     Standard classes of variance function structures (`var-
     Func') 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.

_V_a_l_u_e_:

     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 dif-
          ferent variances according to the levels of a
          classification factor.

varFixed: fixed weights, determined by a variance covariate.

 varComb: combination of variance functions.

_N_o_t_e_:

     Users may define their own `varFunc' classes by speci-
     fying a `constructor' function and, at a minimum, meth-
     ods for the functions `coef', `coef<-', and `initial-
     ize'. For examples of these functions, see the methods
     for class `varPower'.

_A_u_t_h_o_r_(_s_)_:

     Jose Pinheiro and Douglas Bates

_S_e_e _A_l_s_o_:

     `varExp', `varPower', `varConstPower', `varIdent',
     `varFixed', `varComb'

