doc: Ensure documentation lists output argument when it exists for all m-files. For new users of Octave it is best to show explicit calling forms in the documentation and to show a return argument when it exists. * bp-table.cc, shift.m, accumarray.m, accumdim.m, bincoeff.m, bitcmp.m, bitget.m, bitset.m, blkdiag.m, celldisp.m, cplxpair.m, dblquad.m, flip.m, fliplr.m, flipud.m, idivide.m, int2str.m, interpft.m, logspace.m, num2str.m, polyarea.m, postpad.m, prepad.m, randi.m, repmat.m, rng.m, rot90.m, rotdim.m, structfun.m, triplequad.m, uibuttongroup.m, uicontrol.m, uipanel.m, uipushtool.m, uitoggletool.m, uitoolbar.m, waitforbuttonpress.m, help.m, __additional_help_message__.m, hsv.m, im2double.m, im2frame.m, javachk.m, usejava.m, argnames.m, char.m, formula.m, inline.m, __vectorize__.m, findstr.m, flipdim.m, strmatch.m, vectorize.m, commutation_matrix.m, cond.m, cross.m, duplication_matrix.m, expm.m, orth.m, rank.m, rref.m, trace.m, vech.m, cast.m, compare_versions.m, delete.m, dir.m, fileattrib.m, grabcode.m, gunzip.m, inputname.m, license.m, list_primes.m, ls.m, mexext.m, movefile.m, namelengthmax.m, nargoutchk.m, nthargout.m, substruct.m, swapbytes.m, ver.m, verLessThan.m, what.m, fminunc.m, fsolve.m, fzero.m, optimget.m, __fdjac__.m, matlabroot.m, savepath.m, campos.m, camroll.m, camtarget.m, camup.m, camva.m, camzoom.m, clabel.m, diffuse.m, legend.m, orient.m, rticks.m, specular.m, thetaticks.m, xlim.m, xtickangle.m, xticklabels.m, xticks.m, ylim.m, ytickangle.m, yticklabels.m, yticks.m, zlim.m, ztickangle.m, zticklabels.m, zticks.m, ellipsoid.m, isocolors.m, isonormals.m, stairs.m, surfnorm.m, __actual_axis_position__.m, __pltopt__.m, close.m, graphics_toolkit.m, pan.m, print.m, printd.m, __ghostscript__.m, __gnuplot_print__.m, __opengl_print__.m, rotate3d.m, subplot.m, zoom.m, compan.m, conv.m, poly.m, polyaffine.m, polyder.m, polyint.m, polyout.m, polyreduce.m, polyvalm.m, roots.m, prefdir.m, prefsfile.m, profexplore.m, profexport.m, profshow.m, powerset.m, unique.m, arch_rnd.m, arma_rnd.m, autoreg_matrix.m, bartlett.m, blackman.m, detrend.m, durbinlevinson.m, fftconv.m, fftfilt.m, fftshift.m, fractdiff.m, hamming.m, hanning.m, hurst.m, ifftshift.m, rectangle_lw.m, rectangle_sw.m, triangle_lw.m, sinc.m, sinetone.m, sinewave.m, spectral_adf.m, spectral_xdf.m, spencer.m, ilu.m, __sprand__.m, sprand.m, sprandn.m, sprandsym.m, treelayout.m, beta.m, betainc.m, betaincinv.m, betaln.m, cosint.m, expint.m, factorial.m, gammainc.m, gammaincinv.m, lcm.m, nthroot.m, perms.m, reallog.m, realpow.m, realsqrt.m, sinint.m, hadamard.m, hankel.m, hilb.m, invhilb.m, magic.m, pascal.m, rosser.m, toeplitz.m, vander.m, wilkinson.m, center.m, corr.m, cov.m, discrete_cdf.m, discrete_inv.m, discrete_pdf.m, discrete_rnd.m, empirical_cdf.m, empirical_inv.m, empirical_pdf.m, empirical_rnd.m, kendall.m, kurtosis.m, mad.m, mean.m, meansq.m, median.m, mode.m, moment.m, range.m, ranks.m, run_count.m, skewness.m, spearman.m, statistics.m, std.m, base2dec.m, bin2dec.m, blanks.m, cstrcat.m, deblank.m, dec2base.m, dec2bin.m, dec2hex.m, hex2dec.m, index.m, regexptranslate.m, rindex.m, strcat.m, strjust.m, strtrim.m, strtrunc.m, substr.m, untabify.m, __have_feature__.m, __prog_output_assert__.m, __run_test_suite__.m, example.m, fail.m, asctime.m, calendar.m, ctime.m, date.m, etime.m: Add return arguments to @deftypefn macros where they were missing. Rename variables in functions (particularly generic "retval") to match documentation. Rename some return variables for (hopefully) better clarity (e.g., 'ax' to 'hax' to indicate it is a graphics handle to an axes object).

########################################################################
##
## Copyright (C) 2007-2022 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  {} {} ellipsoid (@var{xc}, @var{yc}, @var{zc}, @var{xr}, @var{yr}, @var{zr}, @var{n})
## @deftypefnx {} {} ellipsoid (@dots{}, @var{n})
## @deftypefnx {} {} ellipsoid (@var{hax}, @dots{})
## @deftypefnx {} {[@var{x}, @var{y}, @var{z}] =} ellipsoid (@dots{})
## Plot a 3-D ellipsoid.
##
## The inputs @var{xc}, @var{yc}, @var{zc} specify the center of the ellipsoid.
## The inputs @var{xr}, @var{yr}, @var{zr} specify the semi-major axis lengths.
##
## 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{ellipsoid} returns three matrices in
## @code{meshgrid} format, such that @code{surf (@var{x}, @var{y}, @var{z})}
## generates the ellipsoid.
## @seealso{cylinder, rectangle, sphere}
## @end deftypefn

function [xx, yy, zz] = ellipsoid (varargin)

  [hax, varargin, nargin] = __plt_get_axis_arg__ ("ellipsoid", varargin{:});

  if (nargin != 6 && nargin != 7)
    print_usage ();
  endif

  xc = varargin{1};
  yc = varargin{2};
  zc = varargin{3};
  xr = varargin{4};
  yr = varargin{5};
  zr = varargin{6};

  if (nargin == 6)
    n = 20;
  else
    n = varargin{7};
    if (! (isreal (n) && isscalar (n) && n > 0))
      error ("ellipsoid: N must be a real scalar > 0");
    endif
    n = floor (n);
  endif

  theta = linspace (0, 2 * pi, n + 1);
  phi = linspace (-pi / 2, pi / 2, n + 1);
  [theta, phi] = meshgrid (theta, phi);

  xx = xr .* cos (phi) .* cos (theta) + xc;
  yy = yr .* cos (phi) .* sin (theta) + yc;
  zz = zr .* sin (phi) + zc;

  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;
%! ellipsoid (0, 0, 1, 2, 3, 4, 20);
%! title ("ellipsoid()");

## Test input validation
%!error <Invalid call> ellipsoid (1,2,3,4,5)
%!error <Invalid call> ellipsoid (1,2,3,4,5,6,7,8)
%!error <N must be a real scalar> ellipsoid (1,2,3,4,5,6, 2i)
%!error <N must be a real scalar> ellipsoid (1,2,3,4,5,6, ones (2,2))
%!error <N must be a real scalar . 0> ellipsoid (1,2,3,4,5,6, -1)