# Re: Periodogram and frequency

From: Dennis Shea <shea_at_nyahnyahspammersnyahnyah>
Date: Thu Aug 22 2013 - 09:22:20 MDT

Not sure what is meant by:
"But I want this pick to be over the value 4, not 50. The 4, in this
case, means the frequency with which the 2 repeats"

```---
specx_anal scales the spectra such that the area under
the curve equals the variance of the input series.
This facilitates determining the variance at a particular
frequency interval or at a frequency
fstrt = 0.20
flast = 0.30
ifrq  = ind(frq.ge.fstrt .and. frw.le.flast)
varf  = sum(px*df)
At an individual frequency fstrt=flast  (must be exact)
Attached is a simple script you can use. It uses ezfftf to explicitly
calculate the fourier coefficients and then the periodogram.
do i = 1, dimsizes(listTest21) -1
Should be
do i = 1, dimsizes(listTest21)
but maybe I am wrong.
On 8/22/13 8:17 AM, Rodrigo Colpo wrote:
> Dear all,
>
>
> I have created a list where the number "2" is equally spaced, like this:
>
>
> [0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0]
>
> ... using the following script:
>
>
> Test1 = new(100,integer)
> Test1 = 0
> do i = 1, dimsizes(listTest21) -1
>    if (i%4 .eq. 0) then
>      Test1(i-1 ) = 2
>    end if
> end do
>
> So, every 4 elements, there is one "2".
>
> Then, I used the "specx_anal" function the have information about the "frequency", and ploted the following graph of the periodogram (@spcx):
>
> But I want this pick to be over the value 4, not 50. The 4, in this case, means the frequency with which the 2 repeats (or have oscillations in the "numbers").
>
> The idea is to apply this principle to retrieve information about the time scale needed for clouds to change its "behavior".
>
> Best wishes,
> Rodrigo.
>
>
>
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```

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Received on Thu Aug 22 09:22:25 2013

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