%例程5－11  利用基于AR模型的最大熵法估計功率譜
% e.g.5-11.m for example5-11;
% to test function pyulear;
 
clf;
clear all;
% Generate the signal plus white noise and show
N=1024;
n=0:1/(N-1):1;         %Sampling frequency N-1
f1=0.1;
f2=0.9;
randn('state', 0);    %Set randn to its default initial state
wn=randn(size(n));
xn=sin(2*pi*f1*n)+2*cos(2*pi*f2*n)+wn;
subplot(211);
plot(n,xn); xlabel('n');
grid on;
title(' xn=sin(2*pi*f1*n)+2*cos(2*pi*f2*n)+wn');
% Set parameter
p=50;
nfft=1024;
range='onesided';
% Estimate the PSD using Maximum Entropy Method(MEM)
[Pxx,f]=pyulear(xn,p,nfft,2,range);
subplot(212);
plot(f,10*log10(Pxx )); 
xlabel('Frequency(Hz)');
ylabel('Power Spectrum Density(dB)');
title('PSD with MEM method(order=50)');
grid on;