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########################################################################
##
## Copyright (C) 2012-2025 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 {} {@var{arg} =} nthargout (@var{n}, @var{fcn}, @dots{})
## @deftypefnx {} {@var{arg} =} nthargout (@var{n}, @var{ntot}, @var{fcn}, @dots{})
## Return the @var{n}th output argument of the function specified by the
## function handle or string @var{fcn}.
##
## Any additional arguments are passed directly to @var{fcn}. The total
## number of arguments to call @var{fcn} with can be passed in @var{ntot}; by
## default @var{ntot} is @var{n}. The input @var{n} can also be a vector of
## indices of the output, in which case the output will be a cell array of the
## requested output arguments.
##
## The intended use of @code{nthargout} is to avoid intermediate variables.
## For example, when finding the indices of the maximum entry of a matrix, the
## following two compositions of @code{nthargout}
##
## @example
## @group
## @var{m} = magic (5);
## cell2mat (nthargout ([1, 2], @@ind2sub, size (@var{m}),
## nthargout (2, @@max, @var{m}(:))))
## @result{} 5 3
## @end group
## @end example
##
## @noindent
## are completely equivalent to the following lines:
##
## @example
## @group
## @var{m} = magic (5);
## [~, idx] = max (@var{M}(:));
## [i, j] = ind2sub (size (@var{m}), idx);
## [i, j]
## @result{} 5 3
## @end group
## @end example
##
## It can also be helpful to have all output arguments collected in a single
## cell array as the following code demonstrates:
##
## @example
## @var{USV} = nthargout ([1:3], @@svd, hilb (5));
## @end example
##
## Programming Note: Equivalent functionality to the @code{nthargout} function
## is frequently possible by using the character @samp{~} in code to ignore
## outputs. This functionality is implemented by the Octave interpreter and
## is even more efficient than using this function.
##
## Equivalent Code:
##
## @example
## @group
## idx = nthargout (2, @@max, rand (100, 1));
## @equiv{}
## [~, idx] = max (rand (100, 1));
## @end group
## @end example
##
## @seealso{nargin, nargout, varargin, varargout, isargout}
## @end deftypefn
function arg = nthargout (n, varargin)
if (nargin < 2)
print_usage ();
endif
if (is_function_handle (varargin{1}) || ischar (varargin{1}))
ntot = max (n(:));
fcn = varargin{1};
args = varargin(2:end);
elseif (isnumeric (varargin{1})
&& (is_function_handle (varargin{2}) || ischar (varargin{2})))
ntot = varargin{1};
fcn = varargin{2};
args = varargin(3:end);
else
print_usage ();
endif
if (any (n != fix (n)) || ntot != fix (ntot) || any (n <= 0) || ntot <= 0)
error ("nthargout: N and NTOT must be positive integers");
endif
outargs = cell (1, ntot);
try
[outargs{:}] = feval (fcn, args{:});
if (numel (n) > 1)
arg = outargs(n);
else
arg = outargs{n};
endif
catch
err = lasterror ();
if (strfind (err.message, "some elements undefined in return list"))
error ("nthargout: too many output arguments: %d", ntot);
else
rethrow (err);
endif
end_try_catch
endfunction
%!shared m
%! m = magic (5);
%!
%!assert (nthargout ([1,2], @ind2sub, size (m), nthargout (2, @max, m(:))), {5,3})
%!assert (nthargout (3, @find, m(m>20)), [23, 24, 25, 21, 22]')
## Test input validation
%!error <Invalid call> nthargout ()
%!error <Invalid call> nthargout (1)
%!error <N .* must be positive integers> nthargout (1.5, @sin)
%!error <N .* must be positive integers> nthargout (1, 1.5, @sin)
%!error <N .* must be positive integers> nthargout (0, @sin)
%!error <N .* must be positive integers> nthargout (0, 1, @sin)
%!error <too many output arguments: 2> nthargout (2, @sin, pi)
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