

   CCrreeaattiinngg aanndd CCoonnttrroolllliinngg MMuullttiippllee SSccrreeeennss oonn aa SSiinnggllee DDeevviiccee

        split.screen(figs, screen=<<see below>>, erase=T)
        screen(n=<<see below>>, new=T)
        erase.screen(n=<<see below>>)
        close.screen(n=<<see below>>, all=T)

   AArrgguummeennttss::

       figs: A two-element vector describing the number of rows
             and the number of columns in a screen matrix or a
             matrix with 4 columns.  If a matrix, then each row
             describes a screen with values for the left,
             right, bottom, and top of the screen (in that
             order) in NDC units.

          n: A number indicating which screen to prepare for
             drawing (`screen'), erase (`erase.screen'), or
             close (`close.screen').

        new: A logical value indicating whether the screen
             should be erased as part of the preparation for
             drawing in the screen.

        all: A logical value indicating whether all of the
             screens should be closed.

   DDeessccrriippttiioonn::

        `split.screen' defines a number of regions within the
        current device which can, to some extent, be treated as
        separate graphics devices.  It is useful for generating
        multiple plots on a single device.  Screens can them-
        selves be split, allowing for quite complex arrange-
        ments of plots.

        `screen' is used to select which screen to draw in.

        `erase.screen' is used to clear a single screen.

        `close.screen' removes the specified screen defini-
        tion(s).

   DDeettaaiillss::

        The first call to `split.screen' places R into split-
        screen mode.  The other split-screen functions only
        work within this mode.  While in this mode, certain
        other commands should be avoided (see WARNINGS below).
        Split-screen mode is exited by the command
        `close.screen(all=T)'

   VVaalluuee::

        `split.screen' returns a vector of screen numbers for
        the newly-created screens.  With no arguments,
        `split.screen' returns a vector of valid screen num-
        bers.

        `screen' invisibly returns the number of the selected
        screen.  With no arguments, `screen' returns the number
        of the current screen.

        `close.screen' returns a vector of valid screen num-
        bers.

        `screen', `erase.screen', and `close.screen' all return
        `FALSE' if R is not in split-screen mode.

   WWAARRNNIINNGG::

        These functions are totally incompatible with the other
        mechanisms for arranging plots on a device:
        `par(mfrow)', `par(mfcol)', and `layout()'.

        The functions are also incompatible with some plotting
        functions, such as `coplot', which make use of these
        other mechanisms.

        The functions should not be used with multiple devices.

   SSeeee AAllssoo::

        `par', `layout', `Devices', `dev.*'

   EExxaammpplleess::

        if (interactive()) {

        split.screen(c(2,1))             # split display into two screens
        split.screen(c(1,3), screen = 2) # now split the bottom half into 3
        screen(1) # prepare screen 1 for output
        plot(10:1)
        screen(4) # prepare screen 4 for output
        plot(10:1)
        close.screen(all = T) # exit split-screen mode

        split.screen(c(2,1))        # split display into two screens
        split.screen(c(1,2),2)      # split bottom half in two
        plot(1:10)                  # screen 3 is active, draw plot
        erase.screen()              #forgot label, erase and redraw
        plot(1:10, ylab= "ylab 3")
        screen(1)                 # prepare screen 1 for output
        plot(1:10)
        screen(4)                 # prepare screen 4 for output
        plot(1:10, ylab="ylab 4")
        screen(1, F)              #return to screen 1, but do not clear
        plot(10:1, axes=F, lty=2, ylab="")  # overlay second plot
        axis(4)                   # add tic marks to right-hand axis
        title("Plot 1")
        close.screen(all = T) # exit split-screen mode

        }

