pdIdent                 package:nlme                 R Documentation

_M_u_l_t_i_p_l_e _o_f _t_h_e _I_d_e_n_t_i_t_y _P_o_s_i_t_i_v_e-_D_e_f_i_n_i_t_e _M_a_t_r_i_x

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

     This function is a constructor for the `pdIdent' class,
     representing a multiple of the identity positive-definite matrix. 
     The matrix associated with `object' is represented by 1
     unrestricted parameter, given by the logarithm of the square-root
     of the diagonal value. When `value' is  `numeric(0)', an
     uninitialized `pdMat' object, a one-sided formula, or a vector of
     character strings, `object' is returned as an uninitialized
     `pdIdent' 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 value, it is assumed to represent the unrestricted
     coefficient of the underlying positive-definite  matrix.

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

     pdIdent(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 value. 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 `pdIdent' object representing a multiple of the identity
     positive-definite matrix, 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 <- pdIdent(4 * diag(3), nam = c("A","B","C"))
     pd1

