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25
26## -*- texinfo -*-
27## @deftypefn  {} {} ifftshift (@var{x})
28## @deftypefnx {} {} ifftshift (@var{x}, @var{dim})
29## Undo the action of the @code{fftshift} function.
30##
31## For even length @var{x}, @code{fftshift} is its own inverse, but odd lengths
32## differ slightly.
33## @seealso{fftshift}
34## @end deftypefn
35
36function retval = ifftshift (x, dim)
37
38  if (nargin != 1 && nargin != 2)
39    print_usage ();
40  endif
41
42  if (! (isnumeric (x) || islogical (x) || ischar (x)))
43    error ("ifftshift: X must be a vector or matrix");
44  endif
45
46  if (nargin == 2)
47    if (! (isscalar (dim) && dim > 0 && dim == fix (dim)))
48      error ("ifftshift: dimension DIM must be a positive integer");
49    endif
50    nd = ndims (x);
51    sz = size (x);
52    sz2 = floor (sz(dim) / 2);
53    idx = repmat ({':'}, nd, 1);
54    idx{dim} = [sz2+1:sz(dim), 1:sz2];
55    retval = x(idx{:});
56  else
57    if (isvector (x))
58      xl = length (x);
59      xx = floor (xl/2);
60      retval = x([xx+1:xl, 1:xx]);
61    else
62      nd = ndims (x);
63      sz = size (x);
64      sz2 = floor (sz ./ 2);
65      idx = cell ();
66      for i = 1:nd
67        idx{i} = [sz2(i)+1:sz(i), 1:sz2(i)];
68      endfor
69      retval = x(idx{:});
70    endif
71  endif
72
73endfunction
74
75
76%!test
77%! x = [0:7];
78%! y = ifftshift (x);
79%! assert (y, [4 5 6 7 0 1 2 3]);
80%! assert (ifftshift (y), x);
81
82%!test
83%! x = [0:6];
84%! y = ifftshift (x);
85%! assert (y, [3 4 5 6 0 1 2]);
86%! assert (ifftshift (y), [6 0 1 2 3 4 5]);
87
88%!test
89%! x = [0:7]';
90%! y = ifftshift (x);
91%! assert (y, [4;5;6;7;0;1;2;3]);
92%! assert (ifftshift (y), x);
93
94%!test
95%! x = [0:6]';
96%! y = ifftshift (x);
97%! assert (y, [3;4;5;6;0;1;2]);
98%! assert (ifftshift (y), [6;0;1;2;3;4;5]);
99
100%!test
101%! x = [0:3];
102%! x = [x;2*x;3*x+1;4*x+1];
103%! y = ifftshift (x);
104%! assert (y, [[7 10 1 4];[9 13 1 5];[2 3 0 1];[4 6 0 2]]);
105%! assert (ifftshift (y), x);
106
107%!test
108%! x = [0:3];
109%! x = [x;2*x;3*x+1;4*x+1];
110%! y = ifftshift (x,1);
111%! assert (y, [[1 4 7 10];[1 5 9 13];[0 1 2 3];[0 2 4 6]]);
112%! assert (ifftshift (y,1), x);
113
114%!test
115%! x = [0:3];
116%! x = [x;2*x;3*x+1;4*x+1];
117%! y = ifftshift (x,2);
118%! assert (y, [[2 3 0 1];[4 6 0 2];[7 10 1 4];[9 13 1 5]]);
119%! assert (ifftshift (y,2), x);
120
121%!test
122%! x = "efgabcd";
123%! y = ifftshift (x);
124%! assert (y, "abcdefg");
125%! assert (ifftshift (y), "defgabc");
126
127## Test N-dimensional input
128%!test <*45207>
129%! x = [0:3];
130%! x = x + x' + reshape (x, [1 1 4]);
131%! y1 = [4 5 2 3; 5 6 3 4; 2 3 0 1; 3 4 1 2];
132%! y = ifftshift (x);
133%! assert (y, reshape ([y1 + 2, y1 + 3, y1, y1 + 1], [4 4 4]));
134%! assert (ifftshift (y), x);
135
136## Test input validation
137%!error ifftshift ()
138%!error ifftshift (1, 2, 3)
139%!error ifftshift (0:3, -1)
140%!error ifftshift (0:3, 0:3)
141