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########################################################################
##
## Copyright (C) 2007-2024 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## 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
## <https://www.gnu.org/licenses/>.
##
########################################################################
## -*- texinfo -*-
## @deftypefn {} {} cylinder
## @deftypefnx {} {} cylinder (@var{r})
## @deftypefnx {} {} cylinder (@var{r}, @var{n})
## @deftypefnx {} {} cylinder (@var{hax}, @dots{})
## @deftypefnx {} {[@var{x}, @var{y}, @var{z}] =} cylinder (@dots{})
## Plot a 3-D unit cylinder.
##
## The optional input @var{r} is a vector specifying the radius along the
## unit z-axis. The default is [1 1] indicating radius 1 at @code{Z == 0}
## and at @code{Z == 1}.
##
## The optional input @var{n} determines the number of faces around the
## circumference of the cylinder. The default value is 20.
##
## If the first argument @var{hax} is an axes handle, then plot into this axes,
## rather than the current axes returned by @code{gca}.
##
## If outputs are requested @code{cylinder} returns three matrices in
## @code{meshgrid} format, such that @code{surf (@var{x}, @var{y}, @var{z})}
## generates a unit cylinder.
##
## Example:
##
## @example
## @group
## [x, y, z] = cylinder (10:-1:0, 50);
## surf (x, y, z);
## title ("a cone");
## @end group
## @end example
## @seealso{ellipsoid, rectangle, sphere}
## @end deftypefn
function [x, y, z] = cylinder (varargin)
[hax, args, nargs] = __plt_get_axis_arg__ ("cylinder", varargin{:});
if (nargs > 2)
print_usage ();
elseif (nargs == 0)
r = [1, 1];
n = 20;
elseif (nargs == 1)
r = args{1};
n = 20;
else
r = args{1};
n = args{2};
endif
if (! isvector (r))
error ("cylinder: R must be a scalar or vector");
endif
if (isscalar (r))
r .*= [1 1]; # expand single radius specification to required 2-term form
endif
phi = linspace (0, 2*pi, n+1);
idx = 1:length (r);
[phi, idx] = meshgrid (phi, idx);
zz = (idx - 1) / (length (r) - 1);
r = r(idx);
[xx, yy] = pol2cart (phi, r);
if (nargout > 0)
x = xx;
y = yy;
z = zz;
else
oldfig = [];
if (! isempty (hax))
oldfig = get (0, "currentfigure");
endif
unwind_protect
hax = newplot (hax);
surf (xx, yy, zz);
unwind_protect_cleanup
if (! isempty (oldfig))
set (0, "currentfigure", oldfig);
endif
end_unwind_protect
endif
endfunction
%!demo
%! clf;
%! colormap ("default");
%! [x, y, z] = cylinder (10:-1:0, 50);
%! surf (x, y, z);
%! title ("cylinder() with linearly shrinking radius produces a cone");
## Test input validation
%!error <Invalid call> cylinder (1,2,3)
%!error <R must be a scalar> cylinder ([])
%!error <R must be a scalar or vector> cylinder (ones (2,2))
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