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function coef=ref_zak(f,K)
%-*- texinfo -*-
%@deftypefn {Function} ref_zak
%@verbatim
%REF_ZAK Reference Zak-transform.
% Usage: c=ref_zak(f,K);
%
% This function computes a reference Zak-transform by
% an explicit summation.
%
% It returns the coefficients in the rectangular layout.
%
%@end verbatim
%@strong{Url}: @url{http://ltfat.github.io/doc/reference/ref_zak.html}
%@end deftypefn
% Copyright (C) 2005-2016 Peter L. Soendergaard <peter@sonderport.dk>.
% This file is part of LTFAT version 2.2.0
%
% 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/>.
L=size(f,1);
% Slow, explicit method
% Workspace
coef=zeros(K,L/K);
for jj=0:K-1
for kk=0:L/K-1
for ll=0:L/K-1
coef(jj+1,kk+1)=coef(jj+1,kk+1)+f(mod(jj-ll*K,L)+1)*exp(2*pi*i*kk*ll*K/L);
end;
end;
end;
coef=coef*sqrt(K/L);
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