\name{corBrownian}
\alias{corBrownian}
\alias{coef.corBrownian}
\alias{corMatrix.corBrownian}
\title{Brownian Correlation Structure}
\usage{
	corBrownian(value=1, phy, form=~1)
	\method{coef}{corBrownian}(object, unconstrained = TRUE, ...)
	\method{corMatrix}{corBrownian}(object,
			covariate = getCovariate(object), corr = TRUE, ...)
}
\arguments{
	\item{value}{The \eqn{\gamma}{gamma} parameter (default to 1)}
	\item{phy}{An object of class \code{phylo} representing the phylogeny
		(with branch lengths) to consider}
	\item{object}{An (initialized) object of class \code{corBrownian}}
	\item{corr}{a logical value. If 'TRUE' the function returns the correlation matrix, otherwise it returns
		the variance/covariance matrix.}
	\item{form}{ignored for now.}
	\item{covariate}{ignored for now.}
	\item{unconstrained}{a logical value. If 'TRUE' the coefficients are returned
    in unconstrained form (the same used in the optimization
    algorithm). If 'FALSE' the coefficients are returned in
    "natural", possibly constrained, form. Defaults to 'TRUE'}
	\item{\dots}{some methods for these generics require additional arguments.
		None are used in these methods.}
}
\description{
	Expected covariance under a Brownian model (Felsenstein 1985, Martins and Hansen 1997): 
		\deqn{V_{ij} = \gamma \times t_a}{%
					Vij = gamma . ta}
	where \eqn{t_a}{ta} is the distance on the phylogeny between the root and the most recent common ancestor
	of taxa \eqn{i}{i} and \eqn{j}{j} and \eqn{\gamma}{gamma} is a constant.
}
\value{
	An object of class \code{corBrownian} or coefficient from an object of this class (actually sends \code{numeric(0)}!)
	or the correlation matrix of an initialized object of this class.
}
\author{Julien Dutheil \email{julien.dutheil@univ-montp2.fr}}
\seealso{
  \code{\link{corClasses}}.
}
\references{
  Felsenstein, J. (1985) Phylogenies and the comparative method.
  \emph{American Naturalist}, \bold{125}, 1--15.

  Martins, E. P. and Hansen, T. F. (1997) Phylogenies and the comparative
  method: a general approach to incorporating phylogenetic information
  into the analysis of interspecific data. \emph{American Naturalist},
  \bold{149}, 646--667.
}
\keyword{models}