########################################################################
##
## Copyright (C) 2019-2025 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.
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## under the terms of the GNU General Public License as published by
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########################################################################

## -*- texinfo -*-
## @deftypefn {} {} mustBeNegative (@var{x})
##
## Require that input @var{x} is negative.
##
## Raise an error if any element of the input @var{x} is not negative, as
## determined by @code{@var{x} < 0}.
##
## @seealso{mustBeNonnegative}
## @end deftypefn

function mustBeNegative (x)

  if (nargin < 1)
    print_usage ();
  endif

  tf = (x < 0)(:);
  if (! all (tf))
    label = inputname (1);
    if (isempty (label))
      label = "input";
    endif
    bad_idx = find (! tf);
    try
      bad_val = x(bad_idx);
      errmsg = sprintf ("%s must be negative; found %d elements that were not: values %s", ...
                        label, numel (bad_idx), mat2str (bad_val));
    catch
      errmsg = sprintf ("%s must be negative; found %d elements that were not: indexes %s", ...
                        label, numel (bad_idx), mat2str (bad_idx));
    end_try_catch
    error (errmsg);
  endif

endfunction


%!test
%! mustBeNegative ([]);
%! mustBeNegative (-42);
%! mustBeNegative (-10:-2);

%!error <Invalid call> mustBeNegative ()
%!error <found 1 elements> mustBeNegative ([-1, 42])
%!error <found 6 elements> mustBeNegative (-5:5)
