MATLAB: How to rectify this ‘out of index’ error

out of index error

function [ s ] = harmonic(ms,omegas,damprat,ug,omegax)
ks=ms*omegas^2;
u(1)=0;
u(2)=0;
a(1)=0;
cd=2*ms*omegas*damprat;
k=ms/(0.01)^2+cd/0.02;
x=ms/(0.01)^2-cd/0.02;
y=ks-2*ms/(0.01)^2;
for t=0:0.01:10
    for n=1:1:1001
    if n==(t*100+1)
    p(n)=-ms*ug*sin(omegax*t)-x*u(n)-y*u(n+1);
    u(n+2)=p(n)/k;
    a(n+1)=(u(n+2)-2*u(n+1)+u(n))/(0.01)^2;
    fprintf('t=%5d\t%10.3f\n',t,a(n))
    plot(t,a(n))
    end
    end
end
When I run the above function in command window, I get the following:
harmonic(820.116,7.068,0.014,70,6.283)
t=    0              0.000
t=1.000000e-002      0.000
t=2.000000e-002     -4.352
t=3.000000e-002     -6.449
t=4.000000e-002     -5.280
t=5.000000e-002     -1.471
t=6.000000e-002      3.059
t=7.000000e-002      6.072
t=8.000000e-002      6.123
t=9.000000e-002      3.260
t=1.000000e-001     -1.027
t=1.100000e-001     -4.576
t=1.200000e-001     -5.631
t=1.300000e-001     -3.705
??? Attempted to access u(17); index out of bounds because numel(u)=16.
Error in ==> harmonic at 13
    p(n)=-ms*ug*sin(omegax*t)-x*u(n)-y*u(n+1);
Please suggest why does this happen?
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