varFixed                package: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 function
     structure, also inheriting from class 'varFunc'.

_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:

     'varWeights.varFunc', 'varFunc'

_E_x_a_m_p_l_e_s:

     vf1 <- varFixed(~age)

