

pdDiag(nlme)                                 R Documentation

_D_i_a_g_o_n_a_l _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 `pdDiag' class,
     representing a diagonal positive-definite matrix. If
     the matrix associated with `object' is of dimension n,
     it is represented by n unrestricted parameters, given
     by the logarithm of the square-root of the diagonal
     values. When `value' is `numeric(0)', an uninitialized
     `pdMat' object, a one-sided formula, or a vector of
     character strings, `object' is returned as an unini-
     tialized `pdDiag' 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 con-
     structed from `as.matrix(value)'. Finally, if `value'
     is a numeric vector, it is assumed to represent the
     unrestricted coefficients of the underlying positive-
     definite matrix.

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

     pdDiag(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 equal to
          the dimension of the underlying positive-definite
          matrix. 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 `pdDiag' object representing a diagonal positive-def-
     inite 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_:

     library(nlme)
     pd1 <- pdDiag(diag(1:3), nam = c("A","B","C"))
     pd1

