/usr/share/octave/packages/interval-2.1.0/@infsup/intersect.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
## @defmethod {@@infsup} intersect (@var{A})
## @defmethodx {@@infsup} intersect (@var{A}, @var{B})
## @defmethodx {@@infsup} intersect (@var{A}, [], @var{DIM})
##
## Intersect intervals.
##
## With two arguments the intersection is built pair-wise. Otherwise the
## intersection is computed for all interval members along dimension @var{DIM},
## which defaults to the first non-singleton dimension.
##
## Accuracy: The result is a tight enclosure.
##
## @example
## @group
## x = infsup (1, 3);
## y = infsup (2, 4);
## intersect (x, y)
## @result{} ans = [2, 3]
## @end group
## @end example
## @seealso{@@infsup/union, @@infsup/setdiff, @@infsup/setxor}
## @end defmethod
## Author: Oliver Heimlich
## Keywords: interval
## Created: 2014-10-02
function a = intersect (a, b, dim)
if (not (isa (a, "infsup")))
a = infsup (a);
endif
switch (nargin)
case 1
l = max (a.inf);
u = min (a.sup);
case 2
if (not (isa (b, "infsup")))
b = infsup (b);
endif
l = max (a.inf, b.inf);
u = min (a.sup, b.sup);
case 3
if (not (builtin ("isempty", b)))
warning ("intersect: second argument is ignored");
endif
l = max (a.inf, [], dim);
u = min (a.sup, [], dim);
otherwise
print_usage ();
return
endswitch
## If the intervals do not intersect, the result must be empty.
emptyresult = l > u;
l(emptyresult) = inf;
u(emptyresult) = -inf;
a.inf = l;
a.sup = u;
endfunction
%!# Empty interval
%!assert (intersect (infsup (), infsup ()) == infsup ());
%!assert (intersect (infsup (), infsup (1)) == infsup ());
%!assert (intersect (infsup (0), infsup ()) == infsup ());
%!assert (intersect (infsup (-inf, inf), infsup ()) == infsup ());
%!# Singleton intervals
%!assert (intersect (infsup (0), infsup (1)) == infsup ());
%!assert (intersect (infsup (0), infsup (0)) == infsup (0));
%!# Bounded intervals
%!assert (intersect (infsup (1, 2), infsup (3, 4)) == infsup ());
%!assert (intersect (infsup (1, 2), infsup (2, 3)) == infsup (2));
%!assert (intersect (infsup (1, 2), infsup (1.5, 2.5)) == infsup (1.5, 2));
%!assert (intersect (infsup (1, 2), infsup (1, 2)) == infsup (1, 2));
%!# Unbounded intervals
%!assert (intersect (infsup (0, inf), infsup (-inf, 0)) == infsup (0));
%!assert (intersect (infsup (1, inf), infsup (-inf, -1)) == infsup ());
%!assert (intersect (infsup (-1, inf), infsup (-inf, 1)) == infsup (-1, 1));
%!assert (intersect (infsup (-inf, inf), infsup (42)) == infsup (42));
%!assert (intersect (infsup (42), infsup (-inf, inf)) == infsup (42));
%!assert (intersect (infsup (-inf, 0), infsup (-inf, inf)) == infsup (-inf, 0));
%!assert (intersect (infsup (-inf, inf), infsup (-inf, inf)) == infsup (-inf, inf));
%!# from the documentation string
%!assert (intersect (infsup (1, 3), infsup (2, 4)) == infsup (2, 3));
%!# correct use of signed zeros
%!test
%! x = intersect (infsup (0), infsup (0));
%! assert (signbit (inf (x)));
%! assert (not (signbit (sup (x))));
%!test
%! x = intersect (infsup (0), infsup (0, 1));
%! assert (signbit (inf (x)));
%! assert (not (signbit (sup (x))));
%!test
%! x = intersect (infsup (0, 1), infsup (0));
%! assert (signbit (inf (x)));
%! assert (not (signbit (sup (x))));
%!test
%! x = intersect (infsup (-1, 0), infsup (0, 1));
%! assert (signbit (inf (x)));
%! assert (not (signbit (sup (x))));
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