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\name{is.diagonal.matrix}
\alias{is.diagonal.matrix}
\title{ Test for diagonal square matrix }
\description{
This function returns \code{TRUE} if the given matrix argument x
is a square numeric matrix and that the off-diagonal elements are close
to zero in absolute value to within the given tolerance level. Otherwise,
a \code{FALSE} value is returned.
}
\usage{
is.diagonal.matrix(x, tol = 1e-08)
}
\arguments{
\item{x}{ a numeric square matrix }
\item{tol}{ a numeric tolerance level usually left out }
}
\value{
A TRUE or FALSE value.
}
\references{
Bellman, R. (1987). \emph{Matrix Analysis}, Second edition, Classics in Applied Mathematics,
Society for Industrial and Applied Mathematics.
Horn, R. A. and C. R. Johnson (1990). \emph{Matrix Analysis}, Cambridge University Press.
}
\author{ Frederick Novomestky \email{fnovomes@poly.edu} }
\examples{
A <- diag( 1, 3 )
is.diagonal.matrix( A )
B <- matrix( c( 1, 2, 3, 4 ), nrow=2, byrow=TRUE )
is.diagonal.matrix( B )
C <- matrix( c( 1, 0, 0, 0 ), nrow=2, byrow=TRUE )
is.diagonal.matrix( C )
}
\keyword{ math }
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