function rf=lpcar2rf(ar)
%LPCAR2RF Convert autoregressive coefficients to reflection coefficients AR=(RF)
%
% Input:   ar(:,p+1)  Autoregressive coefficients
% Output:  rf(:,p+1)  Reflection coefficients with rf(:,1)=1


%      Copyright (C) Mike Brookes 1997
%
%      Last modified Fri Dec  3 15:21:40 1999
%
%   VOICEBOX is a MATLAB toolbox for speech processing. Home page is at
%   http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%   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 2 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 can obtain a copy of the GNU General Public License from
%   ftp://prep.ai.mit.edu/pub/gnu/COPYING-2.0 or by writing to
%   Free Software Foundation, Inc.,675 Mass Ave, Cambridge, MA 02139, USA.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

[nf,p1] = size(ar);
if any(ar(:,1)~=1)
  ar=ar./ar(:,ones(1,p1));
end
rf = ar;
w=ones(nf,1);
for j = p1-1:-1:2
  k = rf(:,j+1);
  d = (1-k.^2).^(-1);
  wj=ones(1,j-1);
  rf(:,2:j) = (rf(:,2:j)-k(:,wj).*rf(:,j:-1:2)).*d(:,wj);
end

