

   BBiipplloott ooff MMuullttiivvaarriiaattee DDaattaa

        biplot(x, ...)

        biplot.default(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, ...)

   AArrgguummeennttss::

          x: The `biplot', a fitted object. For
             `biplot.default', the first set of points (a two-
             column matrix), usually associated with observa-
             tions.

          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.

        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 dim-
             name of `x', or `1:n' is the dimname is `NULL'.

      ylabs: A vector of character strings to label the second
             set of points: the default is to use the row dim-
             name of `y', or `1:n' is 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 get the two sets on 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 sup-
             pressed by `arrow.len = 0'.

   DDeessccrriippttiioonn::

        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'.

   SSiiddee EEffffeeccttss::

        a plot is produced on the current graphics device.

   AAuutthhoorr((ss))::

        B.D. Ripley

   RReeffeerreenncceess::

        K. R. Gabriel (1971).  The biplot graphical display of
        matrices with application to principal component analy-
        sis. Biometrika 58, 453-467.

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

   SSeeee AAllssoo::

        `biplot.princomp', also for examples.

