pdCompSymm               package:nlme               R Documentation

_P_o_s_i_t_i_v_e-_D_e_f_i_n_i_t_e _M_a_t_r_i_x _w_i_t_h _C_o_m_p_o_u_n_d _S_y_m_m_e_t_r_y _S_t_r_u_c_t_u_r_e

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

     This function is a constructor for the `pdCompSymm' class,
     representing a positive-definite matrix with compound symmetry
     structure (constant diagonal and constant off-diagonal elements).
     The underlying matrix is represented by 2 unrestricted parameters.
     When `value' is `numeric(0)', an unitialized `pdMat' object, a
     one-sided formula, or a vector of character strings, `object' is
     returned  as an uninitialized `pdCompSymm' object (with just some
     of its  attributes and its class defined) and needs to have its
     coefficients assigned later, generally using the `coef' or
     `matrix' replacement functions. If `value' is an initialized
     `pdMat' object, `object' will be constructed from 
     `as.matrix(value)'. Finally, if `value' is a numeric vector of
     length 2, it is assumed to represent the unrestricted coefficients
     of the underlying positive-definite matrix.

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

     pdCompSymm(value, form, nam, data)

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

   value: an optional initialization value, which can be any of the
          following: a `pdMat' object, a positive-definite matrix, a
          one-sided linear formula (with variables separated by `+'), a
          vector of character strings, or a numeric vector of length 2.
          Defaults to `numeric(0)', corresponding to an uninitialized
          object.

    form: an optional one-sided linear formula specifying the
          row/column names for the matrix represented by `object'.
          Because factors may be present in `form', the formula needs
          to be evaluated on a data.frame to resolve the names it
          defines. This argument is ignored when `value' is a one-sided
          formula. Defaults to `NULL'.

     nam: an optional vector of character strings specifying the
          row/column names for the matrix represented by object. It
          must have  length equal to the dimension of the underlying
          positive-definite matrix and unreplicated elements. This
          argument is ignored when `value' is a vector of character
          strings. Defaults to `NULL'.

    data: an optional data frame in which to evaluate the variables
          named in `value' and `form'. It is used to obtain the levels
          for `factors', which affect the dimensions and the row/column
          names of the underlying matrix. If `NULL', no attempt is made
          to obtain information on  `factors' appearing in the
          formulas. Defaults to the parent frame from which the
          function was called.

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

     a `pdCompSymm' object representing a positive-definite matrix with
     compound symmetry structure, also inheriting from class `pdMat'.

_A_u_t_h_o_r(_s):

     Jose Pinheiro and Douglas Bates

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

     `as.matrix.pdMat', `coef.pdMat', `matrix<-.pdMat'

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

     pd1 <- pdCompSymm(diag(3) + 1, nam = c("A","B","C"))
     pd1

