/usr/share/octave/packages/interval-2.1.0/@infsup/minus.m is in octave-interval 2.1.0-2.
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##
## This program 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.
##
## This program 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 this program; if not, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @documentencoding UTF-8
## @defop Method {@@infsup} minus (@var{X}, @var{Y})
## @defopx Operator {@@infsup} {@var{X} - @var{Y}}
##
## Subtract all numbers of interval @var{Y} from all numbers of @var{X}.
##
## Accuracy: The result is a tight enclosure.
##
## @example
## @group
## x = infsup (2, 3);
## y = infsup (1, 2);
## x - y
## @result{} ans = [0, 2]
## @end group
## @end example
## @seealso{@@infsup/plus}
## @end defop
## Author: Oliver Heimlich
## Keywords: interval
## Created: 2014-09-30
function x = minus (x, y)
if (nargin ~= 2)
print_usage ();
return
endif
if (not (isa (x, "infsup")))
x = infsup (x);
endif
if (not (isa (y, "infsup")))
y = infsup (y);
elseif (isa (y, "infsupdec"))
## Workaround for bug #42735
result = minus (x, y);
return
endif
l = mpfr_function_d ('minus', -inf, x.inf, y.sup);
u = mpfr_function_d ('minus', +inf, x.sup, y.inf);
emptyresult = isempty (x) | isempty (y);
l(emptyresult) = inf;
u(emptyresult) = -inf;
l(l == 0) = -0;
x.inf = l;
x.sup = u;
endfunction
%!# from the documentation string
%!assert (infsup (2, 3) - infsup (1, 2) == infsup (0, 2));
%!# correct use of signed zeros
%!test
%! x = minus (infsup (0), infsup (0));
%! assert (signbit (inf (x)));
%! assert (not (signbit (sup (x))));
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