急需MATLAB程序,用FFT求信号x(t)=sin(40πt)的频谱

急需MATLAB程序,用FFT求信号x(t)=sin(40πt)的频谱
观察采样间隔和长度取不同值时（如T=0.02,0.04；N=100,105）,频谱的变化,判断是否反映信号的真实频谱.

clc; clear ;close all;
T1 = 0.02;
T2 = 0.04;
fs1 = 1/T1;
fs2 = 1/T2;
t1 = 0:T1:20;
t2 = 0:T2:20;
x1 = sin(40*pi*t1);
x2 = sin(40*pi*t2);
y1 = abs(fft(x1));
y2 = abs(fft(x2));
n1 = (1:length(t1))*fs1/length(t1);
n2 = (1:length(t2))*fs2/length(t2);
plot(n1,y1);grid;xlabel('Hz');title('50Hz采样率下的频谱');
figure;plot(n2,y2);grid;xlabel('Hz');title('25Hz采样率下的频谱');
采样率太低,不满足奈奎斯特采样定理,频谱失真.