| 
            plsdiplz
          ( | xmin , | 
| ymin , | |
| xmax , | |
| ymax ); | 
      Set relative minima and maxima incrementally (zoom mode)
      that define the current plot-space window.  This function has
      the same effect as plsdiplt if that function has not been previously
      called.  Otherwise, this function implements zoom mode using the
      transformation min_used = old_min + old_length*min 
      and max_used = old_min + old_length*max  for
      each axis.  For example, if min = 0.05 and
      max = 0.95 for each axis, repeated calls to
      plsdiplz will zoom in by 10 per cent for each call.
    
      Redacted form: plsdiplz(xmin, ymin, xmax, ymax)
    
This function is used in example 31.