clear; clf;
n=[0:1:100]; n2=[0:1:99];
x=cos(0.425*pi*n)+cos(0.615*pi*n)+0.1*(rand(1)-0.5); y2=[x(1:1:100)];
Y=fft(y2,100);
k=[0:1:50];
w=2*pi*k/100;
subplot(2,1,1);
stem(n2,y2); title('signal x(n), 0 <= n <= 99'); xlabel('n');
pause
magY=abs(Y(1:1:51));
plot(w/pi,magY); title('FFT magnitude'); xlabel('frequency in pi units')
% obtaining AR PSDE of a time series
% x = input sequence
% N/2 = number of frequencies
% p = order of AR model
N=100; p=12;
x=detrend(x);
p=input('enter order for AR. p = ');
A=lpc(x,p);
[h,w]=freqz(1,A,N);
y=abs(h);
subplot(2,1,2);
T=num2str(p)
myarg=['AR PSDE magnitude with p=',T]
plot (w/pi,y);
title(myarg); xlabel('frequency in pi units')