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% $Id: pdCompSymm.Rd,v 1.5 2002/03/05 14:59:39 bates Exp $
\name{pdCompSymm}
\title{Positive-Definite Matrix with Compound Symmetry Structure}
\usage{
pdCompSymm(value, form, nam, data)
}
\alias{pdCompSymm}
\arguments{
\item{value}{an optional initialization value, which can be any of the
following: a \code{pdMat} object, a positive-definite
matrix, a one-sided linear formula (with variables separated by
\code{+}), a vector of character strings, or a numeric
vector of length 2. Defaults to \code{numeric(0)}, corresponding to
an uninitialized object.}
\item{form}{an optional one-sided linear formula specifying the
row/column names for the matrix represented by \code{object}. Because
factors may be present in \code{form}, the formula needs to be
evaluated on a data.frame to resolve the names it defines. This
argument is ignored when \code{value} is a one-sided
formula. Defaults to \code{NULL}.}
\item{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
\code{value} is a vector of character strings. Defaults to
\code{NULL}.}
\item{data}{an optional data frame in which to evaluate the variables
named in \code{value} and \code{form}. It is used to
obtain the levels for \code{factors}, which affect the
dimensions and the row/column names of the underlying matrix. If
\code{NULL}, no attempt is made to obtain information on
\code{factors} appearing in the formulas. Defaults to the
parent frame from which the function was called.}
}
\description{
This function is a constructor for the \code{pdCompSymm} class,
representing a positive-definite matrix with compound symmetry
structure (constant diagonal and constant off-diagonal elements). The
underlying matrix is represented by 2 unrestricted parameters.
When \code{value} is \code{numeric(0)}, an unitialized \code{pdMat}
object, a one-sided formula, or a vector of character strings,
\code{object} is returned as an uninitialized \code{pdCompSymm}
object (with just some of its attributes and its class defined) and
needs to have its coefficients assigned later, generally using the
\code{coef} or \code{matrix} replacement functions. If \code{value} is
an initialized
\code{pdMat} object, \code{object} will be constructed from
\code{as.matrix(value)}. Finally, if \code{value} is a numeric vector
of length 2, it is assumed to represent the unrestricted coefficients
of the underlying positive-definite matrix.
}
\value{
a \code{pdCompSymm} object representing a positive-definite
matrix with compound symmetry structure, also inheriting from class
\code{pdMat}.
}
\references{
Pinheiro, J.C., and Bates, D.M. (2000) "Mixed-Effects Models
in S and S-PLUS", Springer, esp. p. 161.
}
\author{Jose Pinheiro \email{Jose.Pinheiro@pharma.novartis.com} and Douglas Bates \email{bates@stat.wisc.edu}}
\seealso{\code{\link{as.matrix.pdMat}},
\code{\link{coef.pdMat}},
\code{\link{matrix<-.pdMat}},
\code{\link{pdClasses}}
}
\examples{
pd1 <- pdCompSymm(diag(3) + 1, nam = c("A","B","C"))
pd1
}
\keyword{models}
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