Array indices must be positive integers or logical values.

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]

Your code works for me with madeup data. Please share the full error message (all the red text). It would also be helpful if you shared what your variable vel is. You can save that to a mat file and attach it to your post usign the paperclip icon.

[C.G.]

I have attached the file and the error.

my error is:

Array indices must be positive integers or logical values.

[Cris LaPierre]

That file is not helpful unfortunately. Can you attached autocorr_test.mat instead?

Answer 1

[G A]

if length(c) is an even number, then (length(c)+1)/2 is not an integer

Answer 2

[Cris LaPierre]

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