## Copyright (C) 2003, 2007 Shai Ayal
##
## 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 3 of the License, 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, see
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} {[@var{c}, @var{lev}] =}  contourc (@var{x}, @var{y}, @var{z}, @var{vn})
## Compute isolines (countour lines) of the matrix @var{z}. 
## Parameters @var{x}, @var{y} and @var{vn} are optional.
##
## The return value @var{lev} is a vector of the contour levels.
## The return value @var{c} is a 2 by @var{n} matrix containing the
## contour lines in the following format
##
## @example
## @var{c} = [lev1, x1, x2, ..., levn, x1, x2, ... 
##      len1, y1, y2, ..., lenn, y1, y2, ...]
## @end example
##
## @noindent
## in which contour line @var{n} has a level (height) of @var{levn} and
## length of @var{lenn}.
## 
## If @var{x} and @var{y} are omitted they are taken as the row/column 
## index of @var{z}.  @var{vn} is either a scalar denoting the number of lines 
## to compute or a vector containing the values of the lines. If only one 
## value is wanted, set @code{@var{vn} = [val, val]};
## If @var{vn} is omitted it defaults to 10.
##
## For example,
## @example
## @group
## x = 0:2;
## y = x;
## z = x' * y;
## contourc (x, y, z, 2:3)
##      @result{}   2.0000   2.0000   1.0000   3.0000   1.5000   2.0000
##      2.0000   1.0000   2.0000   2.0000   2.0000   1.5000
##
## @end group
## @end example
## @seealso{contour}
## @end deftypefn

## Author: shaia

function [c, lev] = contourc (varargin)

  if (nargin == 1)
    vn = 10;
    z = varargin{1};
    x = 1:size(z,2);
    y = 1:size(z,1);
  elseif (nargin == 2)
    vn = varargin{2};
    z = varargin{1};
    x = 1:size(z,2);
    y = 1:size(z,1);
  elseif (nargin == 3)
    vn = 10;
    x = varargin{1};
    y = varargin{2};
    z = varargin{3};
  elseif (nargin == 4)
    vn = varargin{4};
    x = varargin{1};
    y = varargin{2};
    z = varargin{3};
  else
    print_usage ();
  endif

  if (isscalar (vn))
    vv = linspace (min (z(:)), max (z(:)), vn+2)(2:end-1);
  else
    vv = unique (sort (vn));
  endif

  ## Vectorize the x,y vectors, assuming they are output from meshgrid.
  if (! isvector (x))
    x = x(1,:);
  endif

  if (! isvector (y))
    y = y(:,1);
  endif

  ## Make everyone the right dimensions.
  if (size (x, 2) == 1)
    x = x';
  endif
  if (size (y, 2) == 1)
    y = y';
  endif

  ## Now call __contourc__ for the real work...
  c = __contourc__ (x, y, z, vv);
  if (nargout == 2)
    lev = vv;
  endif

endfunction