% File src/library/stats/man/biplot.princomp.Rd
% Part of the R package, https://www.R-project.org
% Copyright 1995-2025 R Core Team
% Distributed under GPL 2 or later

\name{biplot.princomp}
\alias{biplot.princomp}
\alias{biplot.prcomp}
\title{
Biplot for Principal Components
}
\description{
  Produces a biplot (in the strict sense) from the output of
  \code{\link{princomp}} or \code{\link{prcomp}}
}
\usage{
\method{biplot}{prcomp}(x, choices = 1:2, scale = 1, pc.biplot = FALSE, \dots)

\method{biplot}{princomp}(x, choices = 1:2, scale = 1, pc.biplot = FALSE, \dots)
}
\arguments{
  \item{x}{an object of class \code{"princomp"}.}
  \item{choices}{
    length 2 vector specifying the components to plot. Only the default
    is a biplot in the strict sense.
  }
  \item{scale}{
    The variables are scaled by \code{lambda ^ scale} and the
    observations are scaled by \code{lambda ^ (1-scale)} where
    \code{lambda} are the singular values as computed by
    \code{\link{princomp}}.
    Normally \eqn{0 \le \code{scale} \le 1}, and a warning
    will be issued if the specified \code{scale} is outside this range.
  }
  \item{pc.biplot}{
    If true, use what \bibcitet{R:Gabriel:1971} refers to as a
    \dQuote{principal component biplot},
    with \code{lambda = 1} and observations scaled up by sqrt(n) and
    variables scaled down by sqrt(n).  Then inner products between
    variables approximate covariances and distances between observations
    approximate Mahalanobis distance.
  }
  \item{\dots}{optional arguments to be passed to
    \code{\link{biplot.default}}.}
}
\section{Side Effects}{
  a plot is produced on the current graphics device.
}
\details{
  This is a method for the generic function \code{biplot}.  There is
  considerable confusion over the precise definitions: those of the
  original paper, \bibcitet{R:Gabriel:1971}, are followed here.
  \bibcitet{R:Gabriel+Odoroff:1990} use the same definitions, but their
  plots actually correspond to \code{pc.biplot = TRUE}.
}
\references{
  \bibshow{*}
}
\seealso{
    \code{\link{biplot}},
    \code{\link{princomp}}.
}
\examples{
require(graphics)
biplot(princomp(USArrests))
}
\keyword{multivariate}
\keyword{hplot}
