Before any actual plotting calls are made, a graphics program must
      call plinit, is the main initialization routine for PLplot.  It
      sets up all internal data structures necessary for plotting and
      initializes the output device driver.  If the output device has not
      already been specified when plinit is called, a list of valid
      output devices is given and the user is prompted for a choice.
      Either the device number or a device keyword is accepted.
    
      There are several routines affecting the initialization that must
      be called before plinit, if they are used.  The
      function plsdev allows you to set the device explicitly.  The
      function plsetopt allows you to set any command-line option
      internally in your code.  The function plssub may be called to
      divide the output device plotting area into several subpages of equal
    size, each of which can be used separately. 
      One advances to the next page (or screen) via pladv.  If subpages
      are used, this can be used to advance to the next subpage or to a
      particular subpage.