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\name{forceSymmetric-methods}
\title{Force a Matrix to 'symmetricMatrix' Without Symmetry Checks}
%
\docType{methods}
\keyword{array}
\keyword{methods}
%
\alias{forceSymmetric}
\alias{forceSymmetric-methods}
%
\alias{forceSymmetric,CsparseMatrix,character-method}
\alias{forceSymmetric,CsparseMatrix,missing-method}
\alias{forceSymmetric,RsparseMatrix,character-method}
\alias{forceSymmetric,RsparseMatrix,missing-method}
\alias{forceSymmetric,TsparseMatrix,character-method}
\alias{forceSymmetric,TsparseMatrix,missing-method}
\alias{forceSymmetric,denseMatrix,character-method}
\alias{forceSymmetric,denseMatrix,missing-method}
\alias{forceSymmetric,diagonalMatrix,character-method}
\alias{forceSymmetric,diagonalMatrix,missing-method}
\alias{forceSymmetric,indMatrix,character-method}
\alias{forceSymmetric,indMatrix,missing-method}
\alias{forceSymmetric,matrix,character-method}
\alias{forceSymmetric,matrix,missing-method}
%
\description{
Force a square matrix \code{x} to a \code{\linkS4class{symmetricMatrix}},
\bold{without} a symmetry check as it would be applied for \code{as(x,
"symmetricMatrix")}.
}
\usage{
forceSymmetric(x, uplo)
}
\arguments{
\item{x}{any square matrix (of numbers), either \dQuote{"traditional"}
(\code{\link{matrix}}) or inheriting from
\code{\linkS4class{Matrix}}.}
\item{uplo}{optional string, \code{"U"} or \code{"L"} indicating which
\dQuote{triangle} half of \code{x} should determine the result. The
default is \code{"U"} unless \code{x} already has a \code{uplo} slot
(i.e., when it is \code{\linkS4class{symmetricMatrix}}, or
\code{\linkS4class{triangularMatrix}}), where the default will be
\code{x@uplo}.}
}
% \details{
%
% }
\value{
a square matrix inheriting from class
\code{\linkS4class{symmetricMatrix}}.
}
\seealso{\code{\link{symmpart}} for the symmetric part of a matrix, or
the coercions \code{as(x, <symmetricMatrix class>)}.
}
\examples{
## Hilbert matrix
i <- 1:6
h6 <- 1/outer(i - 1L, i, "+")
sd <- sqrt(diag(h6))
hh <- t(h6/sd)/sd # theoretically symmetric
isSymmetric(hh, tol=0) # FALSE; hence
try( as(hh, "symmetricMatrix") ) # fails, but this works fine:
H6 <- forceSymmetric(hh)
## result can be pretty surprising:
(M <- Matrix(1:36, 6))
forceSymmetric(M) # symmetric, hence very different in lower triangle
(tm <- tril(M))
forceSymmetric(tm)
}
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