### Copyright (C) 1996 John W. Eaton
###
### This file is part of Octave.
###
### Octave is free software; you can redistribute it and/or modify it
### under the terms of the GNU General Public License as published by
### the Free Software Foundation; either version 2, or (at your option)
### any later version.
###
### Octave is distributed in the hope that it will be useful, but
### WITHOUT ANY WARRANTY; without even the implied warranty of
### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
### General Public License for more details.
###
### You should have received a copy of the GNU General Public License
### along with Octave; see the file COPYING.  If not, write to the Free
### Software Foundation, 59 Temple Place - Suite 330, Boston, MA
### 02111-1307, USA.

## usage: contour (z, n, x, y)
##
## See also: plot, semilogx, semilogy, loglog, polar, mesh, contour,
##           bar, stairs, gplot, gsplot, replot, xlabel, ylabel, title 

function contour (z, n, x, y)


  if (nargin == 1)
    n = 10;
  endif

  if (nargin == 1 || nargin == 2)
    if (is_matrix (z))
      set nosurface;
      set contour;
      set cntrparam bspline;
      command = sprintf ("set cntrparam levels %d", n);
      eval (command);
      set noparametric;
      set view 0, 0, 1.9, 1;
      gsplot z w l 1;
    else
      error ("mesh: argument must be a matrix");
    endif
  elseif (nargin == 4)
    if (is_vector (x) && is_vector (y) && is_matrix (z))
      xlen = length (x);
      ylen = length (y);
      if (xlen == rows (z) && ylen == columns (z))
        if (rows (x) == 1)
          x = x';
        endif
        len = 3 * ylen;
        zz = zeros (xlen, ylen);
        k = 1;
        for i = 1:3:len
          zz(:,i)   = x;
          zz(:,i+1) = y(k) * ones (xlen, 1);
          zz(:,i+2) = z(:,k);
          k++;
        endfor
        set nosurface;
        set contour;
        set cntrparam bspline;
        command = sprintf ("set cntrparam levels %d", n);
        eval (command);
	set parametric;
        set view 0, 0, 1.9, 1;
	gsplot zz w l 1;
      else
        msg = "mesh: rows (z) must be the same as length (x) and";
        msg = sprintf ("%s\ncolumns (z) must be the same as length (y)", msg);
        error (msg);
      endif
    else
      error ("mesh: x and y must be vectors and z must be a matrix");
    endif    
  else
    usage ("mesh (z, levels, x, y)");
  endif

endfunction