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function [P,f]=mvdr(R,Npoints) 
% Frequency estimate via the MVDR method 
%    [P,f]=music(R,Npoints) returns the pseudo spectrum of a autocorrelation 
%    matrix R in the vector P and Npoints-point frequency vector f.  
% 
% See also : ACORMX, MUSIC 
 
% Copyright by Zhilin Zhang, Hanlin Laboratory 
% $ Revision: 1.0 $  $ Date: 2003/04/04  11:24 $  
 
%   References: 
%     [1] 胡广书，数字信号处理——理论、算法与实现，清华大学出版社，1997 
 
% get dimension of R 
dims=size(R(:,1));     
dim=dims(1); 
 
InvR=inv(R);                            % inverse of R 
deltf=2*pi/Npoints;                     % frequency value between neibor points 
P=zeros(1,Npoints);                     % initialization of P and f 
f=zeros(1,Npoints); 
          
for index=0:Npoints-1 
     
    % design vector a,a=[1 exp(-j*w) exp(-j*w*2) ...exp(-j*w*(dim-1))]'. 
    a=zeros(dim,1); 
    for p=0:dim-1 
        a(p+1)=exp(-j*index*deltf*p); 
    end 
     
    % computer the denominator of Pmvdr 
    psum=a'*InvR*a; 
    P(index+1)=1/psum; 
    f(index+1)=index*deltf; 
end