.\" -*- nroff -*- generated from .Rd format
.BG
.FN pdSymm
.TL
General Positive-Definite Matrix
.DN
This function is a constructor for the `pdSymm' class,
representing a general positive-definite matrix. If the matrix
associated with `object' is of dimension n, it is
represented by n*(n+1)/2 unrestricted parameters,
using the matrix-logarithm parametrization described in Pinheiro and
Bates (1996). 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 `pdSymm' 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,
it is assumed to represent the unrestricted coefficients of the
matrix-logarithm parametrization of the underlying positive-definite
matrix.
.CS
pdSymm(value, form, nam, data)
.OA
.AG 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. Defaults to `numeric(0)', corresponding to an
uninitialized object.
.AG 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'.
.AG 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'.
.AG 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 the formulas. Defaults to the parent
frame from which the function was called.
.RT
a `pdSymm' object representing a general positive-definite
matrix, also inheriting from class `pdMat'.
.SH REFERENCES
Pinheiro, J.C. and Bates., D.M.  (1996) "Unconstrained
Parametrizations for Variance-Covariance Matrices", Statistics and
Computing, 6, 289-296.
.SA
`as.matrix.pdMat', `coef.pdMat',
`matrix<-.pdMat'
.EX
pd1 <- pdSymm(diag(1:3), nam = c("A","B","C"))
pd1
.KW models
.WR
