.\" -*- nroff -*- generated from .Rd format
.BG
.FN pdStrat
.TL
Stratified Positive-Definite Matrix
.DN
This function is a constructor for the `pdStrat' class,
representing a set of positive-definite matrices corresponding to
different strata, defined by `strata'. Different `pdMat'
classes can be used for different strata, but they must all represent
matrices of equal dimensions and equal row/column names.  The number
of coefficients associated with this class is equal to the sum of the
number of coefficients of each `pdMat' object it includes. 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 `pdStrat' 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.
.CS
pdStrat(value, form, nam, data, strata)
.RA
.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, a numeric
vector, or a list of `pdMat' objects, positive-definite
matrices, or numeric vectors. If given as a list, all of its elements
must represent positive-definite matrices of equal dimensions and
equal row/column names, when converted to `pdMat' objects (in
particular, all `pdMat' objects must have the same formula).
When not given as a list, `value' is repeated for all strata.
Defaults to `numeric(0)', corresponding to an uninitialized
object.
.AG form
an optional one-sided linear formula specifying the
row/column names for all `pdMat' objects 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 matrices represented by `object'. It
must have length equal to the dimension of the underlying 
positive-definite matrices 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', `form', and `strata'. 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.
.AG strata
a one-sided formula specifying the stratification variable
for the different `pdMat' objects represented by
`object'. Its right hand side must evaluate to a factor or an
integer in `data'.
.RT
a `pdStrat' object representing a set of positive-definite
matrices corresponding to different strata.

.SA
`pdMat'
.EX
pd1 <- pdStrat(list(pdSymm(diag(2)), pdDiag(c(1,0))), form = ~age,
  data = Orthodont, strata = ~Sex)
pd1
.KW models
.WR
