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## Copyright (C) 2014-2022 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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## -*- texinfo -*-
## @deftypefn {} {} istriu (@var{A})
## Return true if @var{A} is an upper triangular matrix.
##
## An upper triangular matrix has nonzero entries only on the main diagonal and
## above.
## @seealso{isdiag, isbanded, istril, triu, bandwidth}
## @end deftypefn

function retval = istriu (A)

  if (nargin < 1)
    print_usage ();
  endif

  retval = (isnumeric (A) || islogical (A)) && ndims (A) == 2;
  if (retval)
    [i, j] = find (A);
    retval = all (i <= j);
  endif

endfunction


%!assert (! istriu ("string"))
%!assert (istriu ([]))
%!assert (! istriu (zeros (2,2,2)))

%!assert (istriu (1))
%!assert (istriu ([1, 1]))
%!assert (! istriu ([1; 1]))
%!assert (istriu (eye (10)))
%!assert (istriu (speye (100)))

%!assert (istriu (triu (randn (10))))
%!assert (! istriu (randn (10)))

## Test input validation
%!error <Invalid call> istriu ()
