functions in plvp.i -

             plmargin(margin,xy)  
 
   redefines the limits to leave a margin around the inner plot.  
   Margin are in fraction of the plot width. Default 0.05.  
   xy = 1 only sets margin for the x axis.  
   xy = 2 only sets margin for the y axis.  

             plsplit,nx,ny,margin=,style=,dpi=,sys=  
 
   Split the viewport into nx x ny viewports  
   nx = number of horizontal viewports  
   ny = number of vertical viewports  
   margin = margin correction for each viewport (+/- a few hundreth)  
   style = if style is set, the given style is loaded before the  
           split occurs. style can be a string vector of styles, one  
           per viewport to be created.  
   dpi = if dpi is set, the current window is re-created with said dpi  
   sys = system number on which the split operation is to be performed.  
         sys can be used to create complex, multi-level viewports.  
   square = if set, created viewports will be square.  
   vp = a 4 element vector to get a specific viewport, as returned by :  
        get_style,landscape, systems, legends, clegends;  
        write,systems.viewport;  
   height and width as in the call to window.  
          
   examples:  
   plsplit,2,2,style="work.gs"  
     define a 2x2 viewport with style "work.gs"  
   plsplit,2,2,style=["work.gs","work.gs","work.gs","nobox.gs"]  
     define a 2x2 viewport with style "work.gs", except for viewport#4  
     which gets "nobox.gs"  
   plsplit,1,2,sys=2  
     start from graphic system with >1 viewport.  
     viewport#2 will be split in 1x2 sub-viewports  
   plsplit,1,2,sys=2,style=["boxed.gs","nobox.gs"]  
     start from graphic system with >1 viewport.  
     viewport#2 will be split in 1x2 sub-viewports with styles  
     as in the style keyword.  
       
   plsplit,3,3,style=_(array("boxed.gs",7),"nobox.gs","boxed.gs"),\  
     dpi=100,margin=0.005; pljoin,[2,3,5,6]; testViewports;  

             pltitle_vp, title, deltay  
 
     Plot TITLE centered above the coordinate system for any of the  
     standard Gist styles.  You may want to customize this for other  
     plot styles.  
     pos = -1 (left), 0 (default, centered) or 1 (right)  

             xytitles_vp, xtitle, ytitle  
 
       -or- xytitles_vp, xtitle, ytitle, [deltax,deltay]  
     Plot XTITLE horizontally under the viewport and YTITLE vertically  
     to the left of the viewport.  If the tick numbers interfere with  
     the labels, you can specify the [DELTAX,DELTAY] in NDC units to  
     displace the labels.  (Especially for the y title, the adjustment  
     may depend on how many digits the numbers on your scale actually  
     have.)  Note that DELTAX moves YTITLE and DELTAY moves XTITLE.  
     WARNING: There is no easy way to ensure that this type of title  
              will not interfere with the tick numbering.  Interference  
              may make the numbers or the title or both illegible.