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function c = comp_dct(f,type)
%-*- texinfo -*-
%@deftypefn {Function} comp_dct
%@verbatim
%COMP_DCT Calculates DCT
% Input parameters:
% f : Input data.
% type : DCT version.
%
%@end verbatim
%@strong{Url}: @url{http://ltfat.github.io/doc/comp/comp_dct.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/>.
[L,W] = size(f);
switch type
case 1
c=zeros(L,W,assert_classname(f));
f2=[f;flipud(f(2:L-1,:))]/sqrt(2);
f2(1,:)=f2(1,:)*sqrt(2);
f2(L,:)=f2(L,:)*sqrt(2);
s1=fft(f2)/sqrt(2*L-2);
c=s1(1:L,:)+[zeros(1,W);s1(2*L-2:-1:L+1,:);zeros(1,W)];
c(2:L-1,:)=c(2:L-1,:)/sqrt(2);
case 2
c=zeros(L,W,assert_classname(f));
m1=1/sqrt(2)*exp(-(0:L-1)*pi*i/(2*L)).';
m1(1)=1;
m2=1/sqrt(2)*exp((1:L-1)*pi*i/(2*L)).';
s1=fft([f;flipud(f)]);
c=bsxfun(@times,s1(1:L,:),m1)+[zeros(1,W);bsxfun(@times,s1(2*L:-1:L+2,:),m2)];
c=c/sqrt(L)/2;
case 3
c=zeros(2*L,W,assert_classname(f));
m1=1/sqrt(2)*exp(-(0:L-1)*pi*i/(2*L)).';
m1(1)=1;
m2=1/sqrt(2)*exp((L-1:-1:1)*pi*i/(2*L)).';
c=[bsxfun(@times,m1,f);zeros(1,W);bsxfun(@times,m2,f(L:-1:2,:))];
c=fft(c)/sqrt(L);
c=c(1:L,:);
case 4
s1=zeros(2*L,W,assert_classname(f));
c=zeros(L,W,assert_classname(f));
m1=1/sqrt(2)*exp(-(0:L-1)*pi*i/(2*L)).';
m2=1/sqrt(2)*exp((1:L)*pi*i/(2*L)).';
s1=[bsxfun(@times,m1,f);bsxfun(@times,flipud(m2),f(L:-1:1,:))];
s1=exp(-pi*i/(4*L))*fft(s1)/sqrt(2*L);
c=bsxfun(@times,s1(1:L,:),m1)+bsxfun(@times,s1(2*L:-1:L+1,:),m2);
otherwise
error('%s: Type not supported.',upper(mfilename));
end
if isreal(f)
c=real(c);
end;
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