\name{diagReplace}
\alias{diagReplace}
\title{ Replacing Upper or Lower Diagonal of a Correlation or Covariance Matrix}

\description{
The \code{diagReplace} function returns a modified correlation or covariance
matrix by replacing upper diagonal with lower diagonal, or lower diagonal with upper
diagonal.
}

\usage{
diagReplace(R, upper=TRUE)
}

\arguments{
\item{R}{     numeric: correlation or covariance matrix}
\item{upper}{ logical: if \code{TRUE} upper diagonal is replaced with lower
diagonal. If \code{FALSE}, lower diagonal is replaced with upper diagonal.}
}

\value{
\item{R }{ numeric: correlation or covariance matrix }
}

\author{
Gilles Raiche \cr
Centre sur les Applications des Modeles de Reponses aux Items (CAMRI) \cr
Universite du Quebec a Montreal\cr
\email{raiche.gilles@uqam.ca}, \url{http://www.er.uqam.ca/nobel/r17165/}
}

\examples{
# .......................................................
# Example from Kim and Mueller (1978, p. 10)
# Population: upper diagonal
# Simulated sample: lower diagnonal
R <- matrix(c( 1.000, .6008, .4984, .1920, .1959, .3466,
.5600, 1.000, .4749, .2196, .1912, .2979,
.4800, .4200, 1.000, .2079, .2010, .2445,
.2240, .1960, .1680, 1.000, .4334, .3197,
.1920, .1680, .1440, .4200, 1.000, .4207,
.1600, .1400, .1200, .3500, .3000, 1.000),
nrow=6, byrow=TRUE)

# Replace upper diagonal with lower diagonal
RU <- diagReplace(R, upper=TRUE)

# Replace lower diagonal with upper diagonal
RL <- diagReplace(R, upper=FALSE)
# .......................................................
}

\keyword{ manip }