/usr/share/octave/packages/interval-2.1.0/@infsup/sqrrev.m is in octave-interval 2.1.0-2.
This file is owned by root:root, with mode 0o644.
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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
## @deftypemethod {@@infsup} {@var{X} =} sqrrev (@var{C}, @var{X})
## @deftypemethodx {@@infsup} {@var{X} =} sqrrev (@var{C})
##
## Compute the reverse square function.
##
## That is, an enclosure of all @code{x ∈ @var{X}} where
## @code{sqr (x) ∈ @var{C}}.
##
## Accuracy: The result is a tight enclosure.
##
## @example
## @group
## sqrrev (infsup (-2, 1))
## @result{} ans = [-1, +1]
## @end group
## @end example
## @seealso{@@infsup/sqr}
## @end deftypemethod
## Author: Oliver Heimlich
## Keywords: interval
## Created: 2014-10-13
function result = sqrrev (c, x)
if (nargin > 2)
print_usage ();
return
endif
if (nargin < 2)
x = infsup (-inf, inf);
endif
if (not (isa (c, "infsup")))
c = infsup (c);
endif
if (not (isa (x, "infsup")))
x = infsup (x);
endif
p = sqrt (c);
n = -p;
result = union (intersect (p, x), intersect (n, x));
endfunction
%!# from the documentation string
%!assert (sqrrev (infsup (-2, 1)) == infsup (-1, 1));
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