Plot a biplot on the current graphics device.

`biplot(x, …)`# S3 method for default
biplot(x, y, var.axes = TRUE, col, cex = rep(par("cex"), 2),
xlabs = NULL, ylabs = NULL, expand = 1,
xlim = NULL, ylim = NULL, arrow.len = 0.1,
main = NULL, sub = NULL, xlab = NULL, ylab = NULL, …)

x

The `biplot`

, a fitted object. For `biplot.default`

,
the first set of points (a two-column matrix), usually associated
with observations.

y

The second set of points (a two-column matrix), usually associated with variables.

var.axes

If `TRUE`

the second set of points have arrows
representing them as (unscaled) axes.

col

A vector of length 2 giving the colours for the first and
second set of points respectively (and the corresponding axes). If a
single colour is specified it will be used for both sets. If
missing the default colour is looked for in the
`palette`

: if there it and the next colour as used,
otherwise the first two colours of the palette are used.

cex

The character expansion factor used for labelling the points. The labels can be of different sizes for the two sets by supplying a vector of length two.

xlabs

A vector of character strings to label the first set of
points: the default is to use the row dimname of `x`

, or
`1:n`

if the dimname is `NULL`

.

ylabs

A vector of character strings to label the second set of
points: the default is to use the row dimname of `y`

, or
`1:n`

if the dimname is `NULL`

.

expand

An expansion factor to apply when plotting the second set of points relative to the first. This can be used to tweak the scaling of the two sets to a physically comparable scale.

arrow.len

The length of the arrow heads on the axes plotted in
`var.axes`

is true. The arrow head can be suppressed by
`arrow.len = 0`

.

xlim, ylim

Limits for the x and y axes in the units of the first set of variables.

main, sub, xlab, ylab, …

graphical parameters.

a plot is produced on the current graphics device.

A biplot is plot which aims to represent both the observations and
variables of a matrix of multivariate data on the same plot. There are
many variations on biplots (see the references) and perhaps the most
widely used one is implemented by `biplot.princomp`

.
The function `biplot.default`

merely provides the
underlying code to plot two sets of variables on the same figure.

Graphical parameters can also be given to `biplot`

: the size of
`xlabs`

and `ylabs`

is controlled by `cex`

.

K. R. Gabriel (1971).
The biplot graphical display of matrices with application to principal
component analysis.
*Biometrika*, **58**, 453--467.
10.2307/2334381.

J.C. Gower and D. J. Hand (1996).
*Biplots*.
Chapman & Hall.

`biplot.princomp`

, also for examples.