求问matlab 的 In an assignment A(I) = B,the number of elements

求问matlab 的 In an assignment A(I) = B,the number of elements in B and I must be the same.错在啊
clear all;
close all
f(1)=1000;
f(2)=400;
f(3)=60;
a(1)=0.005;
a(2)=0.01;
a(3)=0.02;
f=2000;
t=0:0.001:f-0.001;
for i=1:3;
x(i)=exp(-a(i)*2*pi*f(i)*t).*sin(2*pi*f(i)*t.*sqrt(1-a(i)))
end
for i=1:3
subplot(31i);plot(t,x(i));
end