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+## Copyright (C) 2007 Michael Goffioul
+##
+## 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 2 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, write to the Free Software
+## Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+## 02110-1301  USA
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {[@var{x}, @var{y}, @var{z}] =} sphere (@var{n})
+## @deftypefnx {Function File} {} sphere (@var{h}, @dots{})
+## Generates three matrices in @code{meshgrid} format, such that 
+## @code{surf (@var{x}, @var{y}, @var{z})} generates a unit sphere. 
+## The matrices of @code{@var{n}+1}-by-@code{@var{n}+1}. If @var{n} is 
+## omitted then a default value of 20 is assumed.
+##
+## Called with no return arguments, @code{sphere} call directly 
+## @code{surf (@var{x}, @var{y}, @var{z})}. If an axes handle is passed
+## as the first argument, the the surface is plotted to this set of axes.
+## @seealso{peaks}
+## @end deftypefn
+
+function [xx,yy,zz] = sphere (h, n)
+
+  have_h = false;
+  if (nargin > 1 && isscalar (h) && ishandle (h))
+    if (! strcmp (get (h, "type"), "axes"))
+      error ("sphere: expecting first argument to be an axes object");
+    endif
+    if (nargin == 1)
+      n = 20;
+    endif
+    have_h = true;
+  else
+    if (nargin == 1)
+      n = h;
+    else
+      n = 20;
+    endif
+  endif
+
+  theta = linspace (0, 2*pi, n+1);
+  phi = linspace (-pi/2, pi/2, n+1);
+  [theta,phi] = meshgrid (theta, phi);
+
+  x = cos(phi).*cos(theta);
+  y = cos(phi).*sin(theta);
+  z = sin(phi);
+
+  if (nargout > 0)
+    xx = x;
+    yy = y;
+    zz = z;
+  else
+    if (have_h)
+      oldh = gca ();
+      unwind_protect
+	axes (h);
+	surf (x, y, z);
+      unwind_protect_cleanup
+	axes (oldh);
+      end_unwind_protect
+    else
+      surf (x, y, z);
+    endif
+  endif
+
+endfunction