How to get the absolute value of the a vector inside an array?

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Ana Bianco 2019-9-10

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编辑： Stephen23 2019-9-11

Hi there, I am trying to extract the absolute value of the column vectors inside an array, but it keep giving me the message: Array indices must be positive integers or logical values., for the following code:

absvec = [];
for a = 1:270
    for b =1:10
        abs(H{a,b}) = absvec (a,b),
    end
end

can anyone help me?

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Adam Danz 2019-9-10

编辑：Adam Danz 2019-9-10

Either that's not the error message you're getting or you shared the wrong code with us.

The error message returned by your code is "Index in position 1 exceeds array bounds." (r2019a) Of course this is happeneng because absvec is empty and you're trying to index it.

do you mean

absvec (a,b) = abs(H{a,b}) % ???

Ana Bianco 2019-9-11

I may have confused which came first, thank you!

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Answer 1

Sebastian Körner 2019-9-10

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https://ww2.mathworks.cn/matlabcentral/answers/479700-how-to-get-the-absolute-value-of-the-a-vector-inside-an-array#answer_391234

relly not sure if this is what your question is about but maybe it helps.

since you provided no data to your problem i created some example data myself.

 H ={[5,-6],[5,-6];[7,-8],[7,-8];[5,-6],[5,-6];[7,-8],[7,-8]};
 v=1;
for i=1:4
    for k=1:2
        h(:,v)=abs(H{i,k});
        v=v+1;
    end
end

input: cell array with cevtors in each cell

output: a vector with the absolute values of each vector of the cell array

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Ana Bianco 2019-9-11

That is just perfect! Exactly what I wanted.

Thanks Sebastian!

Stephen23 2019-9-11

编辑：Stephen23 2019-9-11

Simpler and more efficient with a comma-separated list:

>> out = abs(cat(1,H{:}))
out =
6
8
6
8
6
8
6
8

Timing (1e5 iterations):

Elapsed time is 13.833 seconds.  % nested loops
Elapsed time is 2.239 seconds.   % comma-separated list

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