function pf=lpcar2pf(ar,np)
%LPCAR2PF Convert AR coefs to power spectrum PF=(AR,NP)
% the power spectrum will contain np+2 points ranging from Dc to nyquist frequency
% The routine is faster if NP+1 is a power of 2.

%      Copyright (C) Mike Brookes 1998
%      Version: $Id: lpcar2pf.m 2460 2012-10-29 22:20:45Z dmb $
%
%   VOICEBOX is a MATLAB toolbox for speech processing.
%   Home page: http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html
%
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%   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
%   http://www.gnu.org/copyleft/gpl.html or by writing to
%   Free Software Foundation, Inc.,675 Mass Ave, Cambridge, MA 02139, USA.
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[nf,p1]=size(ar);
if nargin<2 np=p1-1; end
pf=abs(rfft(ar.',2*np+2).').^(-2);
if ~nargout
    if nf==1
        plot((0:np+1)/(2*np+2),10*log10(pf));
        xlabel('Normalized frequency f/f_s');
        ylabel('LPC Power Spectrum (dB)');
    end
end

