Cross correlation Between two matrices row by row

Question

Flavia Aluisi 2017-2-23

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https://ww2.mathworks.cn/matlabcentral/answers/326516-cross-correlation-between-two-matrices-row-by-row

编辑： Massimo Zanetti 2017-2-23

Good morning, I have a problem with the cross correlation (crosscorr command), I'm trying to do a cross correlatation btw 2 matrices with dimension 96*3000, and I wrote this small loop:

[r, c] = size(AinO1_correct);

for i=1:r

 [xcf,lags,bounds]=crosscorr(AinO1_correct(i,2) , AinO1_incorrect(:,2));
   correlationAinO1 =  z';
end

but i got this error 'First series must be a vector.' I don't know what is wrong could please help me?

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Answer 1

Massimo Zanetti 2017-2-23

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https://ww2.mathworks.cn/matlabcentral/answers/326516-cross-correlation-between-two-matrices-row-by-row#answer_255994

编辑：Massimo Zanetti 2017-2-23

There are some issues in your code.

crosscorr function requires two vector inputs. Ain01_correct(i,2) it is not (it is a number). Notice also that AinO1_incorrect(:,2) is just the second column of your matrix (not a row).
correlationAinO1 = z'; what is that???

I assume what you want is:

[r, c] = size(AinO1_correct);
for i=1:r
  [xcf,lags,bounds]=crosscorr(AinO1_correct(i,:) , AinO1_incorrect(i,:));
end

notice that arguments of crosscorr function are row vectors from your matrices.

IMPORTANT check the size of the two matrices is the same before running the code.

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Flavia Aluisi 2017-2-23

Thanks, now is working (sorry I'm starting to use matlab), but I have another question, why if I have a matrix 96*3000 I get xcf 1*41 (all Nan) and lags 1*41 (from -20 to 20)?

Massimo Zanetti 2017-2-23

编辑：Massimo Zanetti 2017-2-23

This is due to the fact that having not supplied the number of lags, MATLAB uses a default value numLags=20. Then, the output size is 20*2+1, accordingly.

This is explained in the help page of the function crosscorr, read carefully paragraphs related to numLags input and xcf,lags outputs.

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