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+## Copyright (C) 1993-2012 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);