# How to make time shift in a vector using non integer values?

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Camellia Mouhammad on 11 Jun 2021
Edited: Adam Danz on 14 Jun 2021
I need to implement this equation
I(t-Ts)= co*n(t) +c1* n(t-Ts)
Where Ts is 1 nanosecond, so I keep getting an error " Array indices must be positive or logical values". How can I implement that shift in time? Thank you.
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Camellia Mouhammad on 11 Jun 2021
yes, i'm iterating on t please see the piece of code:
for t =1:10000
nc(t)= sqrt(d0*input(t)+d1)+d2;
I(t)=co*nc(t)+c1*nc(t-Ts)+c2*(nc(t-Ts)^2)+c3*(nc(t-Ts)^3);
end
where Ts is the sampling time choosen to be 1ns, and input is 1x10000 vector

Adam Danz on 11 Jun 2021
I(t-Ts)= co*n(t) +c1* n(t-Ts)
I'm guessing that t has a value of 1 at some point and ts=1 nanosecond, so (t-ts)=0 at some point. As the error message indicates, the array indices must be positive values (or logical values).
Other possibilities are that (t-ts) results in a positive non-integer value or a negative value, both of which cannot be used as indices.
Note that this index problem happens with I(t-Ts) and with n(t-Ts). Without knowing more about what you're doing, I can't provide a more specific solution.
Adam Danz on 13 Jun 2021
Glad I could point you in the right direction. If this answered your question, please consider accepting the answer (blue "accept this answer" button). If you have any other questions on this topic, let us know.