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function cout=comp_dgt_long(f,g,a,M)
%-*- texinfo -*-
%@deftypefn {Function} comp_dgt_long
%@verbatim
%COMP_DGT_LONG Gabor transform using long windows.
% Usage: c=comp_dgt_long(f,g,a,M);
%
% Input parameters:
% f : Factored input data
% g : Window.
% a : Length of time shift.
% M : Number of channels.
% Output parameters:
% c : M x N*W*R array of coefficients, where N=L/a
%
% Do not call this function directly, use DGT instead.
% This function does not check input parameters!
%
% References:
% T. Strohmer. Numerical algorithms for discrete Gabor expansions. In
% H. G. Feichtinger and T. Strohmer, editors, Gabor Analysis and
% Algorithms, chapter 8, pages 267--294. Birkhauser, Boston, 1998.
%
% P. L. Soendergaard. An efficient algorithm for the discrete Gabor
% transform using full length windows. IEEE Signal Process. Letters,
% submitted for publication, 2007.
%
%@end verbatim
%@strong{Url}: @url{http://ltfat.github.io/doc/comp/comp_dgt_long.html}
%@end deftypefn
% Copyright (C) 2005-2016 Peter L. Soendergaard <peter@sonderport.dk>.
% This file is part of LTFAT version 2.3.1
%
% This program is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
%
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
% GNU General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with this program. If not, see <http://www.gnu.org/licenses/>.
% AUTHOR : Peter L. Soendergaard.
gf=comp_wfac(g,a,M);
% Compute the window application
cout=comp_dgt_walnut(f,gf,a,M);
% Apply dft modulation.
cout=fft(cout)/sqrt(M);
% Change to the right shape
L=size(f,1);
W=size(f,2);
N=L/a;
cout=reshape(cout,M,N,W);
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