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function c = comp_dst(f,type)
%-*- texinfo -*-
%@deftypefn {Function} comp_dst
%@verbatim
%COMP_DST Calculates DST
% Input parameters:
% f : Input data.
% type : DST version.
%
%@end verbatim
%@strong{Url}: @url{http://ltfat.github.io/doc/comp/comp_dst.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));
s1=dft([zeros(1,W,assert_classname(f));...
f;...
zeros(1,W,assert_classname(f));...
-flipud(f)]);
% This could be done by a repmat instead.
for w=1:W
c(:,w)=s1(2:L+1,w)-s1(2*L+2:-1:L+3,w);
end;
c=c*1i/2;
case 2
c=zeros(L,W,assert_classname(f));
m1=1/sqrt(2)*exp(-(1:L)*pi*i/(2*L)).';
m1(L)=-i;
m2=-1/sqrt(2)*exp((1:L-1)*pi*i/(2*L)).';
s1=i*fft([f;-flipud(f)])/sqrt(L)/2;
% This could be done by a repmat instead.
for w=1:W
c(:,w)=s1(2:L+1,w).*m1+[s1(2*L:-1:L+2,w).*m2;0];
end;
case 3
c=zeros(2*L,W,assert_classname(f));
m1=1/sqrt(2)*exp((1:L)*pi*i/(2*L)).';
m1(L)=i;
m2=-1/sqrt(2)*exp(-(L-1:-1:1)*pi*i/(2*L)).';
for w=1:W
c(:,w)=[0;m1.*f(:,w);m2.*f(L-1:-1:1,w)];
end;
c=-sqrt(L)*2*i*ifft(c);
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)).';
for w=1:W
s1(:,w)=[m1.*f(:,w);flipud(m2).*f(L:-1:1,w)];
end;
s1=i*exp(-pi*i/(4*L))*fft(s1)/sqrt(2*L);
% This could be done by a repmat instead.
for w=1:W
c(:,w)=s1(1:L,w).*m1+s1(2*L:-1:L+1,w).*m2;
end;
otherwise
error('%s: Type not supported.',upper(mfilename));
end
if isreal(f)
c=real(c);
end;
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