

varFixed(nlme)                               R Documentation

_F_i_x_e_d _V_a_r_i_a_n_c_e _F_u_n_c_t_i_o_n

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

     This function is a constructor for the `varFixed'
     class, representing a variance function with fixed
     variances. Letting v denote the variance covariate
     defined in `value', the variance function s2(v) for
     this class is s2(v)=|v|. The variance covariate v is
     evaluated once at initialization and remains fixed
     thereafter. No coefficients are required to represent
     this variance function.

_U_s_a_g_e_:

     varFixed(value)

_A_r_g_u_m_e_n_t_s_:

   value: a one-sided formula of the form `~ v' specifying a
          variance covariate `v'. Grouping factors are
          ignored.

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

     a `varFixed' object representing a fixed variance func-
     tion structure, also inheriting from class `varFunc'.

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

     Jose Pinheiro and Douglas Bates

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

     `varWeights.varFunc', `varFunc'

_E_x_a_m_p_l_e_s_:

     library(nlme)
     vf1 <- varFixed(~age)

