unfold

UNFOLD Left/right-unfold a 3D array.
   W = UNFOLD(U, DIR) unfolds the 3-dim. tensor U in direction DIR, where 
   DIR is either 'LEFT' or 'RIGHT' (case insensitive).

   See also MATRICIZE, TENSORIZE, TENSORPROD_TTEMPS.

0001 function W = unfold( U, dir )
0002     %UNFOLD Left/right-unfold a 3D array.
0003     %   W = UNFOLD(U, DIR) unfolds the 3-dim. tensor U in direction DIR, where
0004     %   DIR is either 'LEFT' or 'RIGHT' (case insensitive).
0005     %
0006     %   See also MATRICIZE, TENSORIZE, TENSORPROD_TTEMPS.
0007 
0008     %   TTeMPS Toolbox.
0009     %   Michael Steinlechner, 2013-2016
0010     %   Questions and contact: michael.steinlechner@epfl.ch
0011     %   BSD 2-clause license, see LICENSE.txt
0012 
0013     d = size(U);
0014     % pad with 1 for the last dim (annoying)
0015     if length(size(U)) == 2
0016         d = [d, 1];
0017     end
0018 
0019     if strcmpi(dir, 'left')
0020         W = reshape( U, [d(1)*d(2), d(3)] );
0021     elseif strcmpi(dir, 'right')
0022         W = reshape( U, [d(1), d(2)*d(3)] );
0023     else
0024         error('Unknown direction specified. Choose either LEFT or RIGHT') 
0025     end
0026 end