function [b,nshifts] = shiftdim(x,n)
%SHIFTDIM Shift dimensions.
%   B = SHIFTDIM(X,N) shifts the dimensions of X by N.  When N is
%   positive, SHIFTDIM shifts the dimensions to the left and wraps the
%   N leading dimensions to the end.  When N is negative, SHIFTDIM
%   shifts the dimensions to the right and pads with singletons.
%
%   [B,NSHIFTS] = SHIFTDIM(X) returns the array B with the same
%   number of elements as X but with any leading singleton 
%   dimensions removed. NSHIFTS returns the number of dimensions 
%   that are removed. If X is a scalar, SHIFTDIM has no effect.
%
%   SHIFTDIM is handy for creating functions that, like SUM
%   or DIFF, work along the first non-singleton dimension.
%
%   Examples:
%       a = rand(1,1,3,1,2);
%       [b,n]  = shiftdim(a); % b is 3-by-1-by-2 and n is 2.
%       c = shiftdim(b,-n);   % c == a.
%       d = shiftdim(a,3);    % d is 1-by-2-by-1-by-1-by-3.
%
%   See also CIRCSHIFT, RESHAPE, SQUEEZE.

%   Copyright 1984-2004 The MathWorks, Inc. 
%   $Revision: 1.15.4.2 $  $Date: 2004/03/02 21:47:08 $


siz = size(x);
if nargin==1
  n = find(siz~=1,1,'first')-1; % Find leading singleton dimensions
end

if n > 0  % Wrapped shift to the left
  n = rem(n,ndims(x));
end 

if  isempty(n) || isequal(n,0)
  b = x;    % Quick exit if no shift required
  nshifts = 0;
elseif (n > 0)  
  if isequal(siz(1:n),ones(1,n))
    s = [siz ones(1,n+2-length(siz))]; % Leading singletons 
    b = reshape(x,s(n+1:end));
  else
    b = permute(x,[n+1:ndims(x) 1:n]);
  end
else  % Shift to the right (padding with singletons).
    b = reshape(x,[ones(1,-n),siz]);
end
nshifts = n;