| 
            plvpor
          ( | xmin , | 
| xmax , | |
| ymin , | |
| ymax ); | 
      Device-independent routine for setting up the viewport.  This defines
      the viewport in terms of normalized subpage coordinates which run
      from 0.0 to 1.0 (left to right and bottom to top) along each edge of
      the current subpage.  Use the alternate routine plsvpa in order to
      create a viewport of a definite size.
    
xmin
          (PLFLTThe normalized subpage coordinate of the left-hand edge of the viewport.
xmax
          (PLFLTThe normalized subpage coordinate of the right-hand edge of the viewport.
ymin
          (PLFLTThe normalized subpage coordinate of the bottom edge of the viewport.
ymax
          (PLFLTThe normalized subpage coordinate of the top edge of the viewport.
      Redacted form: plvpor(xmin, xmax, ymin, ymax)
    
This function is used in examples 2, 6-8, 10, 11, 15, 16, 18, 21, 23, 24, 26, 27, and 31.