  plvpas(xmin, xmax, ymin, ymax, aspect)
  **************************************

  plvpas

  Device-independent routine for setting up the viewport. The viewport is
  chosen to be the largest with the given aspect ratio that fits within the
  specified region (in terms of normalized subpage coordinates). This routine
  is functionally equivalent to plvpor when a ``natural'' aspect ratio (0.0)
  is chosen. Unlike plvasp, this routine reserves no extra space at the edges
  for labels.

  xmin (PLFLT, input): The normalized subpage coordinate of the left-hand
  edge of the viewport.

  xmax (PLFLT, input): The normalized subpage coordinate of the right-hand
  edge of the viewport.

  ymin (PLFLT, input): The normalized subpage coordinate of the bottom
  edge of the viewport.

  ymax (PLFLT, input): The normalized subpage coordinate of the top edge
  of the viewport.

  aspect (PLFLT, input): Ratio of length of y axis to length of x axis.

