%  ex_12_13_1.m :  習題 12.13

clear all;
close all;

load sunspot.dat;
x=sunspot
x=x-mean(x);
N=length(x);
LEN=4096;
w=0:1/LEN:0.5-1/LEN;    
f=0:1/4096:0.5-1/4096;
%
X=abs(fft(x,LEN));
Psd1=X.^2/N;   
%
subplot(221)
plot(w,Psd1(1:2048));grid on;   

subplot(222)
p_burg1=pBurg(x,3,LEN);
plot(w,p_burg1(1:2048));grid on; 

subplot(223)
p_burg2=pBurg(x,6,LEN);
plot(w,p_burg2(1:2048));grid on; 

subplot(224)
p_burg3=pBurg(x,9,LEN);
plot(w,p_burg3(1:2048));grid on;