td2=linspace(-2*pi,2*pi,5120);
ad2zs=td2.*sin(2*pi*td2);
Y21=fft(ad2zs);
Ts21=td2(2)-td2(1);
Ws21=2*pi/Ts21;
Wn21=Ws21/2;
w21=linspace(0,Wn21,length(td2)/2);
Ya21=abs(Y21(1:length(td2)/2));
plot(w21,Ya21);grid on;
for i=2:length(Ya21)-1
if ((Ya21(i+1)-Ya21(i))/(w21(i+1)-w21(i)))*((Ya21(i)-Ya21(i-1))/(w21(i)-w21(i-1)))<0
        text(w21(i),Ya21(i),[num2str(w21(i))])
    end
end
w21(find(Ya21==max(Ya21)))