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+## Copyright (C) 2010 Ben Abbott and 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 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} {} comet3 (@var{z})
+## @deftypefnx {Function File} {} comet3 (@var{x}, @var{y}, @var{z}, @var{p})
+## @deftypefnx {Function File} {} comet3 (@var{ax}, @dots{})
+## Produce a simple comet style animation along the trajectory provided by 
+## the input coordinate vectors (@var{x}, @var{y}), where @var{x} will default
+## to the indices of @var{y}.
+##
+## The speed of the comet may be controlled by @var{p}, which represents the
+## time which passes as the animation passes from one point to the next.  The
+## default for @var{p} is 0.1 seconds.
+##
+## If @var{ax} is specified the animation is produced in that axis rather than
+## the @code{gca}.
+## @end deftypefn
+
+## Author: jwe
+## Created: 2010-12-17
+
+function comet3 (varargin)
+
+  [h, varargin, nargin] = __plt_get_axis_arg__ ("comet3", varargin{:});
+
+  if (nargin == 0 || nargin == 2 || nargin > 4)
+    print_usage ();
+  elseif (nargin == 1)
+    z = varargin{1};
+    x = y = 1:numel(z);
+    p = 0.1;
+  elseif (nargin == 3)
+    x = varargin{1};
+    y = varargin{2};
+    z = varargin{3};
+    p = 0.1;
+  elseif (nargin == 4)
+    x = varargin{1};
+    y = varargin{2};
+    z = varargin{3};
+    p = varargin{4};
+  endif
+  
+  oldh = gca ();
+  unwind_protect
+    axes (h);
+    newplot ();
+    theaxis = [min(x), max(x), min(y), max(y), min(z), max(z)];
+    num = numel (y);
+    dn = round (num/10);
+    for n = 1:(num+dn);
+      m = n - dn;
+      m = max ([m, 1]);
+      k = min ([n, num]);
+      h = plot3 (x(1:m), y(1:m), z(1:m), "r", x(m:k), y(m:k), z(m:k), "g",
+                 x(k), y(k), z(k), "ob");
+      axis (theaxis);
+      drawnow ();
+      pause (p);
+    endfor
+  unwind_protect_cleanup
+    axes (oldh);
+  end_unwind_protect
+
+endfunction
+
+%!demo
+%! clf
+%! t = 0:pi/20:5*pi;
+%! comet3 (cos(t), sin(t), t, 0.01);