  pladv(sub)
  **********

  pladv

  Advances to the next subpage if sub=0, performing a page advance if there
  are no remaining subpages on the current page. If subwindowing isn't being
  used, pladv(0) will always advance the page. If sub>0, PLplot switches to
  the specified subpage. Note that this allows you to overwrite a plot on the
  specified subpage; if this is not what you intended, use plclr followed by
  plpage to first advance the page. This routine is called automatically
  (with sub=0) by plenv, but if plenv is not used, pladv must be called after
  initializing PLplot but before defining the viewport.

  sub (PLINT, input): Specifies the subpage number (starting from 1 in the
  top left corner and increasing along the rows) to which to advance. Set to
  zero to advance to the next subpage.

