1######################################################################## 2## 3## Copyright (C) 2007-2021 The Octave Project Developers 4## 5## See the file COPYRIGHT.md in the top-level directory of this 6## distribution or <https://octave.org/copyright/>. 7## 8## This file is part of Octave. 9## 10## Octave is free software: you can redistribute it and/or modify it 11## under the terms of the GNU General Public License as published by 12## the Free Software Foundation, either version 3 of the License, or 13## (at your option) any later version. 14## 15## Octave is distributed in the hope that it will be useful, but 16## WITHOUT ANY WARRANTY; without even the implied warranty of 17## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 18## GNU General Public License for more details. 19## 20## You should have received a copy of the GNU General Public License 21## along with Octave; see the file COPYING. If not, see 22## <https://www.gnu.org/licenses/>. 23## 24######################################################################## 25 26## -*- texinfo -*- 27## @deftypefn {} {} cylinder 28## @deftypefnx {} {} cylinder (@var{r}) 29## @deftypefnx {} {} cylinder (@var{r}, @var{n}) 30## @deftypefnx {} {} cylinder (@var{hax}, @dots{}) 31## @deftypefnx {} {[@var{x}, @var{y}, @var{z}] =} cylinder (@dots{}) 32## Plot a 3-D unit cylinder. 33## 34## The optional input @var{r} is a vector specifying the radius along the 35## unit z-axis. The default is [1 1] indicating radius 1 at @code{Z == 0} 36## and at @code{Z == 1}. 37## 38## The optional input @var{n} determines the number of faces around the 39## circumference of the cylinder. The default value is 20. 40## 41## If the first argument @var{hax} is an axes handle, then plot into this axes, 42## rather than the current axes returned by @code{gca}. 43## 44## If outputs are requested @code{cylinder} returns three matrices in 45## @code{meshgrid} format, such that @code{surf (@var{x}, @var{y}, @var{z})} 46## generates a unit cylinder. 47## 48## Example: 49## 50## @example 51## @group 52## [x, y, z] = cylinder (10:-1:0, 50); 53## surf (x, y, z); 54## title ("a cone"); 55## @end group 56## @end example 57## @seealso{ellipsoid, rectangle, sphere} 58## @end deftypefn 59 60function [xx, yy, zz] = cylinder (varargin) 61 62 [hax, args, nargs] = __plt_get_axis_arg__ ("cylinder", varargin{:}); 63 64 if (nargs == 0) 65 r = [1, 1]; 66 n = 20; 67 elseif (nargs == 1) 68 r = args{1}; 69 n = 20; 70 elseif (nargs == 2) 71 r = args{1}; 72 n = args{2}; 73 else 74 print_usage (); 75 endif 76 77 if (length (r) < 2) 78 error ("cylinder: length (R) must be larger than 2"); 79 endif 80 81 phi = linspace (0, 2*pi, n+1); 82 idx = 1:length (r); 83 [phi, idx] = meshgrid (phi, idx); 84 z = (idx - 1) / (length (r) - 1); 85 r = r(idx); 86 [x, y] = pol2cart (phi, r); 87 88 if (nargout > 0) 89 xx = x; 90 yy = y; 91 zz = z; 92 else 93 oldfig = []; 94 if (! isempty (hax)) 95 oldfig = get (0, "currentfigure"); 96 endif 97 unwind_protect 98 hax = newplot (hax); 99 surf (x, y, z); 100 unwind_protect_cleanup 101 if (! isempty (oldfig)) 102 set (0, "currentfigure", oldfig); 103 endif 104 end_unwind_protect 105 endif 106 107endfunction 108 109 110%!demo 111%! clf; 112%! colormap ("default"); 113%! [x, y, z] = cylinder (10:-1:0, 50); 114%! surf (x, y, z); 115%! title ("cylinder() with linearly shrinking radius produces a cone"); 116