cwt and wcoherence different periods

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Elif Cagda Kandemir 2022-3-4

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评论： Elif Cagda Kandemir 2024-1-30

I am performing cwt and wcoherence commands for acceleration responses of two dynamical systems under earthquake motion. Sampling intervals of both systems are same. Hence, the periods obtained from cwt are same for both systems. However they (period_1) differ form period values obtained form wcoherence (period_coh). The codes are below. What is the reason?

Also I cannot achieve same period data (i.e. period_1) in mat file as shown in cwt figures.

[wt1,period_1,coi1] = cwt(accel1(:,m),wname,dt);

[wcoh,wcs,period_coh] = wcoherence(accel1(:,m),accel2(:,m),dt) ;

Thanks in advance.

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Answer 1

vidyesh 2024-1-24

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编辑：vidyesh 2024-1-24

Hi Elif,

You've noticed a difference in the period values when comparing the results from the continuous wavelet transform; cwt and wavelet coherence; wcoherence. This variation is due to the distinct default parameters used to construct the filter banks in each method.

Specifically, the wcoherence function creates its filter bank with the Morlet wavelet, also known as "amor," and sets 'voicesPerOctave' parameter to 12 by default. These parameters influence the period values you obtain.

In contrast, the cwt function uses a different set of default parameters, leading to the period values you've labelled as ‘period_1’ being different from ‘period_coh’.

When calling cwt set the 'wname' parameter as "amor" and 'voicesPerOctave' as 12 to get 'period_1' equal to 'period_coh'.

Hope this helps