# Array indices must be positive integers or logical values.

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C.G. on 27 Sep 2021
Edited: Cris LaPierre on 27 Sep 2021
I keep getting issues saying 'Array indices must be positive integers or logical values', regarding the line ' c(1:(length(c)+1)/2)=[];' in my code. Im struggling to resolve this, can anybody help?
for i = 1:4
if i == 1
res = sqrt(vel(:,1).^2 +vel(:,2).^2 + vel(:,3).^2);
titles = 'resultant GT';
end
if i == 2
res = vel(:,1);
titles = 'u GT';
end
if i == 3
res = vel(:,2);
titles = 'v GT';
end
if i == 4;
res = vel(:,3);
titles = 'w GT';
subplot(4,1,i)
c = smooth(xcorr(res-mean(res)),1800);
c(1:(length(c)+1)/2)=[];
time = find(c<0,1)
plot(c)
xlabel('time')
ylabel('cor')
hold on
plot([1,length(c)],[0,0],'r')
plot([time,time],[min(c),max(c)],'r')
title([titles, ' ,IT - ', num2str(time)])
end
end
Cris LaPierre on 27 Sep 2021

G A on 27 Sep 2021
if length(c) is an even number, then (length(c)+1)/2 is not an integer

Cris LaPierre on 27 Sep 2021
Edited: Cris LaPierre on 27 Sep 2021
Are you getting a warning instead of an error? If so, this means the code still runs, but MATLAB is warning of possible ways to improve your code.
There is a slightly more detailed error message in R2021b. Even though the result of the colon operator is integers in this case, MATLAB prefers the inputs to also be integers when the result is used for indexing, as that is more robust.
c=linspace(0,1,8);
length(c)
ans = 8
1:(length(c)+1)/2 % result is integers
ans = 1×4
1 2 3 4
c(1:(length(c)+1)/2) % Warning that inputs to colon operator should also be integers
Warning: Integer operands are required for colon operator when used as index.
ans = 1×4
0 0.1429 0.2857 0.4286