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function [coef]=comp_dgt_fb(f,g,a,M)
%-*- texinfo -*-
%@deftypefn {Function} comp_dgt_fb
%@verbatim
%COMP_DGT_FB Filter bank DGT
% Usage: c=comp_dgt_fb(f,g,a,M);
%
% This is a computational routine. Do not call it directly.
%
% See help on DGT.
%@end verbatim
%@strong{Url}: @url{http://ltfat.github.io/doc/comp/comp_dgt_fb.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.
% Calculate the parameters that was not specified.
L=size(f,1);
N=L/a;
gl=length(g);
W=size(f,2); % Number of columns to apply the transform to.
glh=floor(gl/2); % gl-half
% Conjugate the window here.
g=conj(fftshift(g));
coef=zeros(M,N,W,assert_classname(f,g));
% ----- Handle the first boundary using periodic boundary conditions. ---
for n=0:ceil(glh/a)-1
% Periodic boundary condition.
fpart=[f(L-(glh-n*a)+1:L,:);...
f(1:gl-(glh-n*a),:)];
fg=bsxfun(@times,fpart,g);
% Do the sum (decimation in frequency, Poisson summation)
coef(:,n+1,:)=sum(reshape(fg,M,gl/M,W),2);
end;
% ----- Handle the middle case. ---------------------
for n=ceil(glh/a):floor((L-ceil(gl/2))/a)
fg=bsxfun(@times,f(n*a-glh+1:n*a-glh+gl,:),g);
% Do the sum (decimation in frequency, Poisson summation)
coef(:,n+1,:)=sum(reshape(fg,M,gl/M,W),2);
end;
% ----- Handle the last boundary using periodic boundary conditions. ---
for n=floor((L-ceil(gl/2))/a)+1:N-1
% Periodic boundary condition.
fpart=[f((n*a-glh)+1:L,:);... % L-n*a+glh elements
f(1:n*a-glh+gl-L,:)]; % gl-L+n*a-glh elements
fg=bsxfun(@times,fpart,g);
% Do the sum (decimation in frequency, Poisson summation)
coef(:,n+1,:)=sum(reshape(fg,M,gl/M,W),2);
end;
% --- Shift back again to make it a frequency-invariant system. ---
for n=0:N-1
coef(:,n+1,:)=circshift(coef(:,n+1,:),n*a-glh);
end;
coef=fft(coef);
% Simple code using a lot of circshifts.
% Move f initially so it lines up with the initial fftshift of the
% window
%f=circshift(f,glh);
%for n=0:N-1
% Do the inner product.
%fg=circshift(f,-n*a)(1:gl,:).*gw;
% Periodize it.
%fpp=zeros(M,W);
%for ii=0:gl/M-1
% fpp=fpp+fg(ii*M+1:(ii+1)*M,:);
%end;
% fpp=sum(reshape(fg,M,gl/M,W),2);
% Shift back again.
% coef(:,n+1,:)=circshift(fpp,n*a-glh); %),M,1,W);
%end;
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