corNatural               package:nlme               R Documentation

_G_e_n_e_r_a_l _c_o_r_r_e_l_a_t_i_o_n _i_n _n_a_t_u_r_a_l _p_a_r_a_m_e_t_e_r_i_z_a_t_i_o_n

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

     This function is a constructor for the `corNatural' class,
     representing a general correlation structure in the ``natural''
     parameterization, which is described under `pdNatural'. Objects
     created using this constructor must later be initialized using the
      appropriate `initialize' method.

_U_s_a_g_e:

     corNatural(value, form, fixed)

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

   value: an optional vector with the parameter values. Default is
          `numeric(0)', which results in a vector of zeros of
          appropriate dimension being assigned to the parameters when
          `object' is initialized (corresponding to an identity
          correlation structure).

    form: a one sided formula of the form `~ t', or `~ t | g',
          specifying a time covariate `t' and,  optionally, a grouping
          factor `g'. A covariate for this correlation structure must
          be integer valued. When a grouping factor is present in
          `form', the correlation structure is assumed to apply only to
          observations within the same grouping level; observations
          with different grouping levels are assumed to be
          uncorrelated. Defaults to `~ 1', which corresponds to using
          the order of the observations in the data as a covariate, and
          no groups.

   fixed: an optional logical value indicating whether the coefficients
          should be allowed to vary in the optimization, or kept fixed
          at their initial value. Defaults to `FALSE', in which case
          the coefficients are allowed to vary.

_V_a_l_u_e:

     an object of class `corNatural' representing a general correlation
     structure.

_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:

     `initialize.corNatural', `pdNatural'

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

     ## covariate is observation order and grouping factor is Subject
     cs1 <- corNatural(form = ~ 1 | Subject)

