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25
26## -*- texinfo -*-
27## @deftypefn  {} {@var{y} =} shiftdim (@var{x}, @var{n})
28## @deftypefnx {} {[@var{y}, @var{ns}] =} shiftdim (@var{x})
29## Shift the dimensions of @var{x} by @var{n}, where @var{n} must be
30## an integer scalar.
31##
32## When @var{n} is positive, the dimensions of @var{x} are shifted to the left,
33## with the leading dimensions circulated to the end.  If @var{n} is negative,
34## then the dimensions of @var{x} are shifted to the right, with @var{n}
35## leading singleton dimensions added.
36##
37## Called with a single argument, @code{shiftdim}, removes the leading
38## singleton dimensions, returning the number of dimensions removed in the
39## second output argument @var{ns}.
40##
41## For example:
42##
43## @example
44## @group
45## x = ones (1, 2, 3);
46## size (shiftdim (x, -1))
47##   @result{}   1   1   2   3
48## size (shiftdim (x, 1))
49##   @result{}   2   3
50## [b, ns] = shiftdim (x)
51##   @result{} b =
52##         1   1   1
53##         1   1   1
54##   @result{} ns = 1
55## @end group
56## @end example
57## @seealso{reshape, permute, ipermute, circshift, squeeze}
58## @end deftypefn
59
60function [y, ns]  = shiftdim (x, n)
61
62  if (nargin < 1 || nargin > 2)
63    print_usage ();
64  endif
65
66  nd = ndims (x);
67  orig_dims = size (x);
68
69  if (nargin == 1)
70    ## Find the first non-singleton dimension.
71    (n = find (orig_dims != 1, 1) - 1) || (n = nd);
72  elseif (! (isscalar (n) && n == fix (n)))
73    error ("shiftdim: N must be a scalar integer");
74  endif
75
76  if (n >= nd)
77    n = rem (n, nd);
78  endif
79
80  if (n < 0)
81    singleton_dims = ones (1, -n);
82    y = reshape (x, [singleton_dims, orig_dims]);
83  elseif (n > 0)
84    ## We need permute here instead of reshape to shift values in a
85    ## compatible way.
86    y = permute (x, [n+1:nd 1:n]);
87  else
88    y = x;
89  endif
90
91  ns = n;
92
93endfunction
94
95
96%!test
97%! x = rand (1, 1, 4, 2);
98%! [y, ns] = shiftdim (x);
99%! assert (size (y), [4 2]);
100%! assert (ns, 2);
101%! assert (shiftdim (y, -2), x);
102%! assert (size (shiftdim (x, 2)), [4 2]);
103
104%!assert (size (shiftdim (rand (0, 1, 2))), [0 1 2])
105
106## Test input validation
107%!error (shiftdim ())
108%!error (shiftdim (1,2,3))
109%!error (shiftdim (1, ones (2)))
110%!error (shiftdim (1, 1.5))
111