interpreting xcorr for time series plots

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CG
CG on 10 Sep 2024
Commented: Jatin on 12 Sep 2024
i'm using xcorr to work out the lag between two time series.
When I plot the results of xcorr, and ask it to return the maximum lag, the result I get is -58.3.
This is the maximum positive c value, but the spike at 0 into negative c values is the largest overall - is this the result i should be using instead?

Answers (1)

Jatin
Jatin on 10 Sep 2024
Edited: Jatin on 10 Sep 2024
Hi @CG,
The result you should choose depends on the context of your analysis. The "xcorr" function represents "the similarity between a vector x and shifted (lagged) copies of a vector y as a function of the lag." If your goal is to find the exact shift needed to align the signals, you should select the highest correlation value, whether it occurs at a positive or negative lag.
Since you mentioned that the spike at lag 0 is the largest, this indicates the signals are best aligned without any shift. Therefore, if you're looking for the best overall alignment, you can use the lag at 0.
Refer the below documentation on "xcorr" for more details on how the function works:
Hope this helps!
  2 Comments
CG
CG on 10 Sep 2024
Thanks for replying.
I got confused with the documentation as the examples only show postive correlation values, whereas my plots show positive and negative.
I am looking for the best overall alignment, so therefore I should choose the largest spike in the plot, whether that occurs at a positive or negative correlation value.
Thanks

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