--- /dev/null
+## Copyright (C) 2009 Javier Enciso <j4r.e4o@gmail.com>
+##
+## This program 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.
+##
+## This program 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
+## this program; if not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function file} {@var{x}, @var{y}} z_curve (@var{n})
+## Creates an iteration of the Z-order space-filling curve with @var{n} points.
+## The argument @var{n} must be of the form @code{2^M}, where @var{m} is an
+## integer greater than 0.
+##
+## @example
+## n = 8
+## [x ,y] = z_curve (n);
+## line (x, y, "linewidth", 4, "color", "blue");
+## @end example
+##
+## @end deftypefn
+
+function [x, y] = z_curve (n)
+
+ if (nargin != 1)
+ print_usage ();
+ endif
+
+ check_power_of_two (n);
+ if (n == 2)
+ x = [0, 1, 0, 1];
+ y = [0, 0, -1, -1];
+ else
+ [x1, y1] = z_curve (n/2);
+ x2 = n/2 + x1;
+ y2 = y1 - n/2;
+ x = [x1, x2, x1, x2];
+ y = [y1, y1, y2, y2];
+ endif
+
+endfunction
+
+function check_power_of_two (n)
+ if (frac_part (log (n) / log (2)) != 0)
+ error ("z_curve: input argument must be a power of 2.")
+ endif
+endfunction
+
+function d = frac_part (f)
+ d = f - floor (f);
+endfunction
+
+%!test
+%! n = 2;
+%! expect = [0, 1, 0, 1; 0, 0, -1, -1];
+%! [get(1,:), get(2,:)] = z_curve (n);
+%! if (any(size (expect) != size (get)))
+%! error ("wrong size: expected %d,%d but got %d,%d", size (expect), size (get));
+%! elseif (any (any (expect!=get)))
+%! error ("didn't get what was expected.");
+%! endif
+
+%!test
+%! n = 5;
+%!error z_curve (n);
+
+%!demo
+%! clf
+%! n = 4;
+%! [x, y] = z_curve (n);
+%! line (x, y, "linewidth", 4, "color", "blue");
+%! % -----------------------------------------------------------------------
+%! % the figure window shows an iteration of the Z-order space-fillig curve
+%! % with 4 points on each axis.
+
+%!demo
+%! clf
+%! n = 32;
+%! [x, y] = z_curve (n);
+%! line (x, y, "linewidth", 2, "color", "blue");
+%! % ----------------------------------------------------------------------
+%! % the figure window shows an iteration of the Z-order space-fillig curve
+%! % with 32 points on each axis.