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## Copyright (C) 1993-2013 John W. Eaton
##
## This file is part of Octave.
##
## Octave 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.
##
## Octave 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 Octave; see the file COPYING. If not, see
## <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {} rot90 (@var{A})
## @deftypefnx {Function File} {} rot90 (@var{A}, @var{k})
## Return a copy of @var{A} with the elements rotated counterclockwise in
## 90-degree increments. The second argument is optional, and specifies
## how many 90-degree rotations are to be applied (the default value is 1).
## Negative values of @var{k} rotate the matrix in a clockwise direction.
## For example,
##
## @example
## @group
## rot90 ([1, 2; 3, 4], -1)
## @result{} 3 1
## 4 2
## @end group
## @end example
##
## @noindent
## rotates the given matrix clockwise by 90 degrees. The following are all
## equivalent statements:
##
## @example
## @group
## rot90 ([1, 2; 3, 4], -1)
## rot90 ([1, 2; 3, 4], 3)
## rot90 ([1, 2; 3, 4], 7)
## @end group
## @end example
##
## Note that @code{rot90} only works with 2-D arrays. To rotate N-D arrays
## use @code{rotdim} instead.
## @seealso{rotdim, flipud, fliplr, flipdim}
## @end deftypefn
## Author: jwe
function B = rot90 (A, k = 1)
if (nargin < 1 || nargin > 2)
print_usage ();
endif
if (ndims (A) > 2)
error ("rot90: A must be a 2-D array");
elseif (! (isscalar (k) && isreal (k) && k == fix (k)))
error ("rot90: K must be a single real integer");
endif
k = mod (k, 4);
if (k == 0)
B = A;
elseif (k == 1)
B = flipud (A.');
elseif (k == 2)
B = flipud (fliplr (A));
elseif (k == 3)
B = (flipud (A)).';
else
error ("rot90: internal error!");
endif
endfunction
%!test
%! x1 = [1, 2; 3, 4];
%! x2 = [2, 4; 1, 3];
%! x3 = [4, 3; 2, 1];
%! x4 = [3, 1; 4, 2];
%!
%! assert (rot90 (x1), x2);
%! assert (rot90 (x1, 2), x3);
%! assert (rot90 (x1, 3), x4);
%! assert (rot90 (x1, 4), x1);
%! assert (rot90 (x1, 5), x2);
%! assert (rot90 (x1, -1), x4);
%% Test input validation
%!error rot90 ()
%!error rot90 (1, 2, 3)
%!error rot90 (1, ones (2))
%!error rot90 (1, 1.5)
%!error rot90 (1, 1+i)
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