varClasses               package: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 ('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.

_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 different
          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 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'.

_A_u_t_h_o_r(_s):

     Jose Pinheiro Jose.Pinheiro@pharma.novartis.com and Douglas Bates
     bates@stat.wisc.edu

_S_e_e _A_l_s_o:

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

