clear;
clc;
t=0:0.001:2;
n=2001;
Fs=1000;
Fc=200;
x=cos(2*pi*Fc*t);
y1=fft(x);
y2=fftshift(y1);
f=(0:2000)*Fs/n-Fs/2;
hold on;
plot(f,abs(y1),'r')
plot(f,abs(y2),'b')