https://github.com/cran/Matrix
Tip revision: 2e0067f9722efc8b4b804cd331e4d6289b44e966 authored by Doug and Martin on 12 August 2011, 00:00:00 UTC
version 0.9996875-3
version 0.9996875-3
Tip revision: 2e0067f
facmul.Rd
\name{facmul}
\title{Multiplication by Decomposition Factors}
\usage{
facmul(x, factor, y, transpose, left, \dots)
}
\alias{facmul}
\alias{facmul.default}
\description{
Performs multiplication by factors for certain decompositions (and
allows explicit formation of those factors).
}
\arguments{
\item{x}{
a matrix decomposition.
No missing values or IEEE special values are allowed.
}
\item{factor}{
an indicator for selecting a particular factor for multiplication.
}
\item{y}{
a matrix or vector to be multiplied by the factor or its transpose.
No missing values or IEEE special values are allowed.
}
\item{transpose}{
a logical value. When \code{FALSE} (the default) the factor is
applied. When \code{TRUE} the transpose of the factor is applied.
}
\item{left}{
a logical value. When \code{TRUE} (the default) the factor is
applied from the left. When \code{FALSE} the factor is applied
from the right.
}
\item{...}{
the method for \code{"qr.Matrix"} has additional arguments.
}
}
\value{
the product of the selected factor (or its transpose) and \code{y}
}
\section{NOTE}{
Factors for decompositions such as \code{lu} and \code{qr} can be
stored in a compact form.
The function \code{facmul} allows multiplication without explicit
formation of the factors, saving both storage and operations.
}
\references{
Golub, G., and Van Loan, C. F. (1989).
\emph{Matrix Computations,}
2nd edition, Johns Hopkins, Baltimore.
}
% \seealso{
% \code{\link{facmul.lu.Matrix}}, \code{\link{facmul.lu.Hermitian}}, \code{\link{facmul.qr.Matrix}}, \code{\link{expand}}.
% }
\examples{
library(Matrix)
x <- Matrix(rnorm(9), 3, 3)
\dontrun{
qrx <- qr(x) # QR factorization of x
y <- rnorm(3)
facmul( qr(x), factor = "Q", y) # form Q y
}
}
\keyword{array}
\keyword{algebra}