  plmesh(x, y, z, nx, ny, opt)
  ****************************

  plmesh

  Plots a surface mesh within the environment set up by plw3d. The surface
  is defined by the two-dimensional array z  , the point z[i][j] being the
  value of the function at (x[i], y[j]). Note that the points in arrays x and
  y do not need to be equally spaced, but must be stored in ascending order.
  The parameter opt controls the way in which the surface is displayed. For
  further details 3-d Plots.

  x (PLFLT *, input): Pointer to set of x coordinate values at which the
  function is evaluated.

  y (PLFLT *, input): Pointer to set of y coordinate values at which the
  function is evaluated.

  z (PLFLT **, input): Pointer to a vectored two-dimensional array with
  set of function values.

  nx (PLINT, input): Number of x values at which function is evaluated.

  ny (PLINT, input): Number of y values at which function is evaluated.

  opt (PLINT, input): Determines the way in which the surface is
  represented:

   o 1: Lines are drawn showing z as a function of x for each value of y[j].
   o 2: Lines are drawn showing z as a function of y for each value of x[i].
   o 3: Network of lines is drawn connecting points at which function is
     defined.

  mx (PLINT, input): Length of array in x direction, for plotting
  subarrays (Fortran only).

