Array indices must be positive integers or logical values.

Question

C.G. 2021-9-27

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https://ww2.mathworks.cn/matlabcentral/answers/1461589-array-indices-must-be-positive-integers-or-logical-values

编辑： Cris LaPierre 2021-9-27

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

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C.G. 2021-9-27

编辑：C.G. 2021-9-27

在 MATLAB Online 中打开

autocorr_test.m

I have attached the file and the error.

my error is:

Array indices must be positive integers or logical values.

Cris LaPierre 2021-9-27

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

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Answer 1

G A 2021-9-27

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

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Answer 2

Cris LaPierre 2021-9-27

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1461589-array-indices-must-be-positive-integers-or-logical-values#answer_796149

编辑：Cris LaPierre 2021-9-27

在 MATLAB Online 中打开

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