function Px = music(x,p,M)
%MUSIC	Frequency estimation using the MUSIC algorithm.
%-----
%USAGE	Px=music(x,p,M)
%
%	The input sequence x is assumed to consist of p complex
%	exponentials in white noise.  The frequencies of the
%	complex exponentials and the variance of the white noise
%	are estimated using the MUSIC algorithm.  
%
%	x : input sequence
%       p : number of complex exponentials to find
%	M : number of noise eigenvectors to use
%
%	The frequency estimates are found from the peaks of the
%	pseudospectrum Px.
%
%  see also PHD, EV, and MIN_NORM
%
%---------------------------------------------------------------
% copyright 1996, by M.H. Hayes.  For use with the book 
% "Statistical Digital Signal Processing and Modeling"
% (John Wiley & Sons, 1996).
%---------------------------------------------------------------

   x   = x(:);
   if M<p+1 | length(x)<M, error('Size of R is inappropriate'), end
   R = covar(x,M);
   [v,d]=eig(R);
   [y,i]=sort(diag(d));
   Px=0;
   for j=1:M-p
       Px=Px+abs(fft(v(:,i(j)),1024));
       end;
   Px=-20*log10(Px);
   end;