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## -*- texinfo -*-
## @deftypefn  {} {@var{x} =} ifftshift (@var{y})
## @deftypefnx {} {@var{x} =} ifftshift (@var{y}, @var{dim})
## Undo the action of the @code{fftshift} function.
##
## For even length @var{x}, @code{fftshift} is its own inverse, but odd lengths
## differ slightly.
## @seealso{fftshift}
## @end deftypefn

function x = ifftshift (y, dim)

  if (nargin < 1)
    print_usage ();
  endif

  if (! (isnumeric (y) || islogical (y) || ischar (y)))
    error ("ifftshift: Y must be a vector or matrix");
  endif

  if (nargin == 2)
    if (! (isscalar (dim) && dim > 0 && dim == fix (dim)))
      error ("ifftshift: dimension DIM must be a positive integer");
    endif
    nd = ndims (y);
    sz = size (y);
    sz2 = floor (sz(dim) / 2);
    idx = repmat ({':'}, nd, 1);
    idx{dim} = [sz2+1:sz(dim), 1:sz2];
    x = y(idx{:});
  else
    if (isvector (y))
      yl = length (y);
      y2 = floor (yl/2);
      x = y([y2+1:yl, 1:y2]);
    else
      nd = ndims (y);
      sz = size (y);
      sz2 = floor (sz ./ 2);
      idx = cell ();
      for i = 1:nd
        idx{i} = [sz2(i)+1:sz(i), 1:sz2(i)];
      endfor
      x = y(idx{:});
    endif
  endif

endfunction


%!test
%! x = [0:7];
%! y = ifftshift (x);
%! assert (y, [4 5 6 7 0 1 2 3]);
%! assert (ifftshift (y), x);

%!test
%! x = [0:6];
%! y = ifftshift (x);
%! assert (y, [3 4 5 6 0 1 2]);
%! assert (ifftshift (y), [6 0 1 2 3 4 5]);

%!test
%! x = [0:7]';
%! y = ifftshift (x);
%! assert (y, [4;5;6;7;0;1;2;3]);
%! assert (ifftshift (y), x);

%!test
%! x = [0:6]';
%! y = ifftshift (x);
%! assert (y, [3;4;5;6;0;1;2]);
%! assert (ifftshift (y), [6;0;1;2;3;4;5]);

%!test
%! x = [0:3];
%! x = [x;2*x;3*x+1;4*x+1];
%! y = ifftshift (x);
%! assert (y, [[7 10 1 4];[9 13 1 5];[2 3 0 1];[4 6 0 2]]);
%! assert (ifftshift (y), x);

%!test
%! x = [0:3];
%! x = [x;2*x;3*x+1;4*x+1];
%! y = ifftshift (x,1);
%! assert (y, [[1 4 7 10];[1 5 9 13];[0 1 2 3];[0 2 4 6]]);
%! assert (ifftshift (y,1), x);

%!test
%! x = [0:3];
%! x = [x;2*x;3*x+1;4*x+1];
%! y = ifftshift (x,2);
%! assert (y, [[2 3 0 1];[4 6 0 2];[7 10 1 4];[9 13 1 5]]);
%! assert (ifftshift (y,2), x);

%!test
%! x = "efgabcd";
%! y = ifftshift (x);
%! assert (y, "abcdefg");
%! assert (ifftshift (y), "defgabc");

## Test N-dimensional input
%!test <*45207>
%! x = [0:3];
%! x = x + x' + reshape (x, [1 1 4]);
%! y1 = [4 5 2 3; 5 6 3 4; 2 3 0 1; 3 4 1 2];
%! y = ifftshift (x);
%! assert (y, reshape ([y1 + 2, y1 + 3, y1, y1 + 1], [4 4 4]));
%! assert (ifftshift (y), x);

## Test input validation
%!error <Invalid call> ifftshift ()
%!error ifftshift (0:3, -1)
%!error ifftshift (0:3, 0:3)