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Re: [Tftb-help] Help, why 'morlet' and 'a' expressions are of this form

 From: François AUGER Subject: Re: [Tftb-help] Help, why 'morlet' and 'a' expressions are of this form in tfrscalo? Date: Fri, 11 Mar 2011 09:27:22 +0100

```Dear Ting Xu,

At 03:45 10/03/2011, ting xu wrote:
```
```Greetings all,
```
I am trying to use wavelet method to analyze the brain signal. I found the results from 'tfrscalo' and 'cwt' were different. It is difficult for me to understand the following questions: (1) In tfrscalo, the script showed that the morlet wavelet was generated by ha = exp(-(2*log(10)/nha^2)*tha.^2).*exp(i*2*pi*f(ptr)*tha). Should the morlet be exp(-x^2/2)*cos(5*x)?
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I think that exp(-x^2/2)*cos(5*x) is the Mexican hat wavelet, not the Morlet Wavelet.
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(2) the scale 'a' and the frequency 'f' have a relationship f=fc*fs/a, here fc is the center frequency of a wavelet, fs is the sampling frequency. But in tfrscalo, f = logspace(log10(fmin),log10(fmax),N), a = logspace(log10(fmax/fmin),log10(1),N), it does not seem to satisfy f=fc*fs/a. I have confused about it.
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The dilation factor is adimensional. If you multiply fc by fs, the result will be in s^{-2}, and can't be equal to the frequency f.
```I am not sure to be able to understand your question.

Best regards,

```
```Can anyone help me please? Much appreciate!

Best regards,
Ting Xu

--
Xu,Ting
Neuropsychology and Applied Cognitive Neuroscience (NACN) Lab
Institute of Psychology
Beijing 100101
China
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Francois Auger,  http://www.univ-nantes.fr/auger-f

Departement Mesures Physiques de l'IUT de Saint-Nazaire, bureau 2108
tel : 02 40 17 81 20, internet : http://www.univ-nantes.fr/iutsn/mp

Laboratoire Ireena, Crtt, bureau 272
tel : 02 40 17 26 35, internet : http://www.polytech.univ-nantes.fr/ireena

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