t=0:0.001:2*pi;
y=sin(t).*sin(2*t);
Y=fft(y,1024);
f=(0:1023)*2*pi/1024;
plot(f,abs(Y));
axis([-0.1 2*pi+0.1 0 500]);
title('sin(t).*sin(2*t)频谱');
