  plbox3(xopt, xlabel, xtick, nxsub, yopt, ylabel, ytick, nysub, zopt, zlabel,
  ****************************************************************************
  ztick, nzsub)
  *************

  plbox3

  Draws axes, numeric and text labels for a three-dimensional surface plot.
  For a more complete description of three-dimensional plotting 3-d Plots.

  xopt (char *, input): Pointer to character string specifying options for
  the x axis. The string can include any combination of the following letters
  (upper or lower case) in any order:

   o b: Draws axis at base, at height z=zmin where zmin is defined by call to
     plw3d. This character must be specified in order to use any of the other
     options.
   o i: Inverts tick marks, so they are drawn downwards, rather than upwards.
   o l: Labels axis logarithmically. This only affects the labels, not the
     data, and so it is necessary to compute the logarithms of data points
     before passing them to any of the drawing routines.
   o n: Writes numeric labels at major tick intervals.
   o s: Enables subticks between major ticks, only valid if t is also
     specified.
   o t: Draws major ticks.
   o u: If this is specified, the text label for the axis is written under the
     axis.

  xlabel (char *, input): Pointer to character string specifying text
  label for the x axis. It is only drawn if u is in the xopt string.

  xtick (PLFLT, input): World coordinate interval between major ticks on
  the x axis. If it is set to zero, PLplot automatically generates a suitable
  tick interval.

  nxsub (PLINT, input): Number of subintervals between major x axis ticks
  for minor ticks. If it is set to zero, PLplot automatically generates a
  suitable minor tick interval.

  yopt (char *, input): Pointer to character string specifying options for
  the y axis. The string is interpreted in the same way as xopt.

  ylabel (char *, input): Pointer to character string specifying text
  label for the y axis. It is only drawn if u is in the yopt string.

  ytick (PLFLT, input): World coordinate interval between major ticks on
  the y axis. If it is set to zero, PLplot automatically generates a suitable
  tick interval.

  nysub (PLINT, input): Number of subintervals between major y axis ticks
  for minor ticks. If it is set to zero, PLplot automatically generates a
  suitable minor tick interval.

  zopt (char *, input): Pointer to character string specifying options for
  the z axis. The string can include any combination of the following letters
  (upper or lower case) in any order:

   o b: Draws z axis to the left of the surface plot.
   o c: Draws z axis to the right of the surface plot.
   o d: Draws grid lines parallel to the x-y plane behind the figure. These
     lines are not drawn until after plot3d or plmesh are called because of
     the need for hidden line removal.
   o i: Inverts tick marks, so they are drawn away from the center.
   o l: Labels axis logarithmically. This only affects the labels, not the
     data, and so it is necessary to compute the logarithms of data points
     before passing them to any of the drawing routines.
   o m: Writes numeric labels at major tick intervals on the right-hand
     verical axis.
   o n: Writes numeric labels at major tick intervals on the left-hand verical
     axis.
   o s: Enables subticks between major ticks, only valid if t is also
     specified.
   o t: Draws major ticks.
   o u: If this is specified, the text label is written beside the left-hand
     axis.
   o v: If this is specified, the text label is written beside the right-hand
     axis.

  zlabel (char *, input): Pointer to character string specifying text
  label for the z axis. It is only drawn if u or v are in the zopt string.

  ztick (PLFLT, input): World coordinate interval between major ticks on
  the z axis. If it is set to zero, PLplot automatically generates a suitable
  tick interval.

  nzsub (PLINT, input): Number of subintervals between major z axis ticks
  for minor ticks. If it is set to zero, PLplot automatically generates a
  suitable minor tick interval.

