.\" -*- nroff -*- generated from .Rd format
.BG
.FN pdIdent
.TL
Multiple of the Identity Positive-Definite Matrix
.DN
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.
.CS
pdIdent(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
value. 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 in the formulas. Defaults to the
parent frame from which the function was called.
.RT
a `pdIdent' object representing a multiple of the identity
positive-definite matrix, also inheriting from class `pdMat'.

.SA
`as.matrix.pdMat', `coef.pdMat',
`matrix<-.pdMat'
.EX
pd1 <- pdIdent(4 * diag(3), nam = c("A","B","C"))
pd1
.KW models
.WR
