## Copyright 2014 Oliver Heimlich
## Copyright 2017 Joel Dahne
##
## 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} isempty (@var{X})
##
## Check if the interval represents the empty set.
##
## Evaluated on interval arrays, this functions is applied element-wise.
##
## Warning: This function is not compatible with the builtin @code{isempty}
## function.
##
## @seealso{@@infsup/eq, @@infsup/isentire, @@infsup/issingleton}
## @end defmethod

## Author: Oliver Heimlich
## Keywords: interval
## Created: 2014-09-27

function result = isempty (x)

  if (nargin ~= 1)
    print_usage ();
    return
  endif

  result = (x.inf > x.sup);

endfunction

%!assert (isempty (infsup ()));
%!assert (not (isempty (infsup (1, 2))));

%!shared testdata
%! # Load compiled test data (from src/test/*.itl)
%! testdata = load (file_in_loadpath ("test/itl.mat"));

%!test
%! # Scalar evaluation
%! testcases = testdata.NoSignal.infsup.isEmpty;
%! for testcase = [testcases]'
%!   assert (isequaln (...
%!     isempty (testcase.in{1}), ...
%!     testcase.out));
%! endfor

%!test
%! # Vector evaluation
%! testcases = testdata.NoSignal.infsup.isEmpty;
%! in1 = vertcat (vertcat (testcases.in){:, 1});
%! out = vertcat (testcases.out);
%! assert (isequaln (isempty (in1), out));

%!test
%! # N-dimensional array evaluation
%! testcases = testdata.NoSignal.infsup.isEmpty;
%! in1 = vertcat (vertcat (testcases.in){:, 1});
%! out = vertcat (testcases.out);
%! # Reshape data
%! i = -1;
%! do
%!   i = i + 1;
%!   testsize = factor (numel (in1) + i);
%! until (numel (testsize) > 2)
%! in1 = reshape ([in1; in1(1:i)], testsize);
%! out = reshape ([out; out(1:i)], testsize);
%! assert (isequaln (isempty (in1), out));
