x=linspace(1,10,512);
y=exp(-0.01*x).*cos(2*x)+2*exp(-0.015*x).*sin(10*x);
Y = fft(y,512);
Pyy = abs(Y);  
f = 500*(0:255)/512;
plot(f,Pyy(1:256))
pp=Pyy(1:256);
hold on
b=find(diff(sign(diff(pp)))<0)+1;% 求解极值点序号
plot(f(b), pp(b),'r*')
for i=1:length(b)
text(f(b(i)), pp(b(i)),[num2str(floor(f(b(i)))),'Hz'])
end