# Array indices must be positive integers or logical values MATLAB error

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Lucas Larese De Santo on 10 May 2020
Why do I keep getting an error "Array indices must be positive integers or logical values"?
m1=100; m2=50; k1=7410; k2=8230; b1=1430; b2=153;
A=[0 1 0 0;
-(k1+k2)/m1 -(b1+b2)/m1 k2/m1 b2/m1;
0 0 0 1;
k2/m2 b2/m2 -k2/m2 -b2/m2];
B=[0 0;
k1/m1 b1/m1
0 0;
0 0];
C=[1 0 0 0;
0 0 1 0;
k1/m1 b1/m1 0 0;
-k2/m2 -b2/m2 k2/m2 b2/m2];
D=[0 0;
0 0
k1/m1 b1/m1
0 0];
h0=0.05;
t0=1;
w=2*pi/t0;
t=0:0.01:4;
z0=h0*sin(w*t).*(0<=t & t<t0)
z0dot=h0*w*cos(w*t).*(0<=t & t<t0);
sys=ss(A,B,C,D);
lsim(sys,z0(t),t)
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Walter Roberson on 10 May 2020
I notice you compute z0dot but you do not use it?

Toder on 10 May 2020
z0(t) is causing the error. t is a vector of decimals, and you cannot use a decimal as an index. Indices must be positive integers, or logical values, as the error mentions.
Lucas Larese De Santo on 10 May 2020
Ok thank you. So what I could thereotically do is for my input for the lsim use [z0;z0dot] then? You also mention z0 should be a 401 x 2, why is that instead of a 2 x 401?