\name{LU-class}
\docType{class}
\alias{LU-class}
\alias{denseLU-class}
\alias{expand,denseLU-method}
\title{LU (dense) Matrix Decompositions}
\description{
  The \code{"LU"} class is the \emph{virtual} class of LU decompositions of
  real matrices.  \code{"denseLU"} the class of LU decompositions of
  dense real matrices.
}
\section{Objects from the Class}{
  Objects can be created by calls of the form \code{new("denseLU", ...)}.
  More commonly the objects are created explicitly from calls of the form
  \code{\link{lu}(mm)} where \code{mm} is an object that inherits from the
  \code{"dgeMatrix"} class or as a side-effect of other functions applied
  to \code{"dgeMatrix"} objects.
}
\section{Extends}{
  \code{"LU"} directly extends the virtual class
  \code{"\linkS4class{MatrixFactorization}"}.

  \code{"denseLU"} directly extends \code{"LU"}.
}
\section{Slots}{
  \describe{
    \item{\code{x}:}{object of class \code{"numeric"}.  The \code{"L"}
      (unit lower triangular) and \code{"U"} (upper triangular) factors
      of the original matrix.  These are stored in a packed format
      described in the Lapack manual.}
    \item{\code{perm}:}{Object of class \code{"integer"} - a vector of
      length \code{min(Dim)} that describes the permutation applied to
      the rows of the original matrix.  The contents of this vector are
      described in the Lapack manual.}
    \item{\code{Dim}:}{the dimension of the original matrix; inherited
      from class \code{\linkS4class{MatrixFactorization}} .}
  }
}
\section{Methods}{
  \describe{
    \item{expand}{\code{signature(x = "denseLU")}: Produce the \code{"L"} and
      \code{"U"} factors as a named list of matrices.}
  }
}
% \references{}
% \author{}
% \note{}
\seealso{
  class \code{\linkS4class{sparseLU}} for LU decompositions of
  \emph{sparse} matrices;
  further, class \code{\linkS4class{dgeMatrix}} and functions \code{\link{lu}},
  \code{\link{expand}}.
}
\examples{
set.seed(1)
mm <- Matrix(round(rnorm(9),2), nrow = 3)
mm
str(lum <- lu(mm))
elu <- expand(lum)
elu # three components: "L", "U", and "P", the permutation
elu$L \%*\% elu$U
(m2 <- with(elu, P \%*\% L \%*\% U)) # the same as 'mm'
stopifnot(all.equal(as(mm, "matrix"),
                    as(m2, "matrix")))
}
\keyword{classes}
\keyword{algebra}