[ncl-talk] Fourier decompose
Soma Roy
somaroy892 at gmail.com
Tue Feb 26 10:39:48 MST 2019
Please ignore last mail.
Soma
On Tue, Feb 26, 2019, 22:44 Soma Roy <somaroy892 at gmail.com wrote:
> Hello,
> What will be the size of "x" in the below line when I have 135 lon. and
> 129 lat. as in the input dataset?
>
> x = *random_normal* <http://www.ncl.ucar.edu/Document/Functions/Built-in/random_normal.shtml>( 10, 5, (/ntim,nlat,mlon/) )
> xNew = new( *dimsizes*(x), "float")
>
> Kindly inform me.
>
> Soma
>
>
> On Mon, Feb 25, 2019, 23:18 Soma Roy <somaroy892 at gmail.com wrote:
>
>> So if we use fft2df, spatial extent will be reduced in output matrix?
>> I can save coef., split coef. into real and imaginary part..but that is
>> not the issue I am looking for.
>>
>> Kindly inform me.
>>
>> Soma
>>
>>
>>
>> On Mon, Feb 25, 2019, 14:26 Soma Roy <somaroy892 at gmail.com wrote:
>>
>>> As per the below;
>>>
>>> ntim = 8
>>> nlat = 6
>>> mlon = 8
>>> x = *random_normal* <http://www.ncl.ucar.edu/Document/Functions/Built-in/random_normal.shtml>( 10, 5, (/ntim,nlat,mlon/) )
>>> xNew = new( *dimsizes*(x), "float")
>>>
>>> do nt=0,ntim-1
>>> ; ANALYSIS
>>>
>>> coef = *fft2df* (x(nt,:,:_) ; *coef: ; [2] x [6] x [5] ; [2] x [nlat] x [mlon/2+1]*
>>> ; do something with coef *<== *YOUR* responsibility*
>>>
>>> xNew(nt,:,:) = *fft2db* <http://www.ncl.ucar.edu/Document/Functions/Built-in/fft2db.shtml> (coef) ; SYNTHESIS
>>>
>>> end do
>>>
>>> We can see that longitude is reduced from 8 to 5..
>>>
>>> Can we place time dimension on that place keeping latxlon as total grid points in the 2 nd dimension?
>>>
>>> Otherwise at the time of spatial plot, no.of grids will be short due to the reduction along longitude.
>>>
>>> Kindly inform me about the above issue.
>>>
>>> Let me know if I am thinking wrong in it.
>>>
>>>
>>> Thanking you,
>>>
>>> Soma
>>>
>>>
>>>
>>>
>>> On Sat, Feb 23, 2019, 04:02 Gus Correa <gus at ldeo.columbia.edu wrote:
>>>
>>>> Just follow the very clear script outline that Dennis sent to you.
>>>> And where he wrote:
>>>>
>>>> >> ; do something with coef *<== *YOUR* responsibility*
>>>>
>>>> take responsibility and do it.
>>>> Maybe, create a 4D array of dimensions (time, 2, k_lon, k_lat), (or if
>>>> you prefer (2,time,k_lon,k_lat) ),
>>>> where k_lon, k_lat are the corresponding wavenumber index dimension
>>>> sizes, and for each time record,
>>>> save the output of fft2df in the corresponding (time, :, :, :) array
>>>> section/slice.
>>>> You may want to read the fft2df documentation to understand what you're
>>>> doing, and create the array
>>>> to store what the function returns (complex numbers, separated in real
>>>> and imaginary parts) with the correct size:
>>>>
>>>> http://www.ncl.ucar.edu/Document/Functions/Built-in/fft2df.shtml
>>>>
>>>> On Fri, Feb 22, 2019 at 3:37 PM Soma Roy <somaroy892 at gmail.com> wrote:
>>>>
>>>>> Then how can I proceed?
>>>>> Please give me a hint..
>>>>>
>>>>> Soma
>>>>>
>>>>> On Sat, Feb 23, 2019, 00:47 Gus Correa <gus at ldeo.columbia.edu wrote:
>>>>>
>>>>>> If what you want is the *spatial* 2D Fourier Transform
>>>>>> (" fourier decomposition ... over lat lon", as stated in your
>>>>>> original email),
>>>>>> i.e., if you're interested in the 2D wavenmuber components (not in
>>>>>> the time frequencies)
>>>>>> you have to do it separately for each time record, as Dennis
>>>>>> explained.
>>>>>>
>>>>>> You can apply the 2D Fourier Transform function to the 2D array
>>>>>> formed by the reshaped
>>>>>> lat,lon coordinates (into a 1D array) concatenated over the time
>>>>>> dimension,
>>>>>> because all you need to apply a 2D Fourier transform is a 2D
>>>>>> numerical array,
>>>>>> regardless of the meaning of the array components.
>>>>>> However, the result won't be the " fourier decomposition ... over lat
>>>>>> lon" that you said you want.
>>>>>>
>>>>>> I hope this helps,
>>>>>> Gus Correa
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Fri, Feb 22, 2019 at 1:24 PM Soma Roy <somaroy892 at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> Best idea will be use nlat*nlon as total grid points using reshape
>>>>>>> and reorder the data so that input to the fft2df will be 2 dimensional
>>>>>>> (ngrids, ntim).
>>>>>>>
>>>>>>> Coef will then give you output as 2 x ngrids x (ntim/2+1).
>>>>>>>
>>>>>>> Soma
>>>>>>>
>>>>>>> On Fri, Feb 22, 2019, 21:32 Soma Roy <somaroy892 at gmail.com wrote:
>>>>>>>
>>>>>>>> Glad to know.
>>>>>>>> Many thanks Dennis.
>>>>>>>>
>>>>>>>> Soma
>>>>>>>>
>>>>>>>> On Fri, Feb 22, 2019, 21:09 Dennis Shea <shea at ucar.edu wrote:
>>>>>>>>
>>>>>>>>> *Please do not send direct emails to people. Only to ncl-talk.*
>>>>>>>>>
>>>>>>>>> If "X" is the data then how can we use it?
>>>>>>>>>
>>>>>>>>> X (ntime, nlat, nlon).
>>>>>>>>>
>>>>>>>>> Output result matrix should be same as X.
>>>>>>>>> ==============
>>>>>>>>>
>>>>>>>>> *As noted in the documentation, *the function is prototyped as
>>>>>>>>> 2-dimensional
>>>>>>>>>
>>>>>>>>> *function fft2df ( x [*][*])*
>>>>>>>>>
>>>>>>>>> As I said, you must use a do loop. It is user (your)
>>>>>>>>> responsibility to do any book keepind [savinh]
>>>>>>>>>
>>>>>>>>> ntim = 8
>>>>>>>>> nlat = 6
>>>>>>>>> mlon = 8
>>>>>>>>> x = *random_normal* <http://www.ncl.ucar.edu/Document/Functions/Built-in/random_normal.shtml>( 10, 5, (/ntim,nlat,mlon/) )
>>>>>>>>> xNew = new( *dimsizes*(x), "float")
>>>>>>>>>
>>>>>>>>> do nt=0,ntim-1
>>>>>>>>> ; ANALYSIS
>>>>>>>>> coef = *fft2df* (x(nt,:,:_) ; *coef: [2] x [6] x [5] ; [2] x [nlat] x [mlon/2+1]*
>>>>>>>>>
>>>>>>>>> ; do something with coef *<== *YOUR* responsibility*
>>>>>>>>>
>>>>>>>>> xNew(nt,:,:) = *fft2db* <http://www.ncl.ucar.edu/Document/Functions/Built-in/fft2db.shtml> (coef) ; SYNTHESIS
>>>>>>>>>
>>>>>>>>> end do
>>>>>>>>>
>>>>>>>>> Please do not use this if you do not know how to use 2D FFT output.
>>>>>>>>> ncl-talk can not become your programmer.
>>>>>>>>>
>>>>>>>>> Again, as noted in the function documentation, a readable introduction to 2D-FFT is at:
>>>>>>>>> *http://www.dspguide.com/pdfbook.htm* <http://www.dspguide.com/pdfbook.htm>
>>>>>>>>> ===
>>>>>>>>> As noted in the documentation, NCL uses* FFTPACK5 <https://www2.cisl.ucar.edu/resources/legacy/fft5> *developed by Paul Swarztrauber and Richard Valent.
>>>>>>>>> The specific Fortran subroutines used are:
>>>>>>>>> * fft2df:
>>>>>>>>> http://www2.cisl.ucar.edu/resources/legacy/fft5/documentation#rfft2f.html <http://www2.cisl.ucar.edu/resources/legacy/fft5/documentation#rfft2f.html>
>>>>>>>>>
>>>>>>>>> fft2db:
>>>>>>>>> http://www2.cisl.ucar.edu/resources/legacy/fft5/documentation#rfft2b.html <http://www2.cisl.ucar.edu/resources/legacy/fft5/documentation#rfft2b.html>
>>>>>>>>> *
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Fri, Feb 22, 2019 at 8:06 AM Soma Roy <somaroy892 at gmail.com>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> If "X" is the data then how can we use it?
>>>>>>>>>>
>>>>>>>>>> X (ntime, nlat, nlon).
>>>>>>>>>>
>>>>>>>>>> Output result matrix should be same as X.
>>>>>>>>>>
>>>>>>>>>> Soma
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Fri, Feb 22, 2019, 20:24 Dennis Shea <shea at ucar.edu wrote:
>>>>>>>>>>
>>>>>>>>>>> Please look at NCL's function documentation
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> *http://www.ncl.ucar.edu/Document/Functions/Built-in/fft2df.shtml
>>>>>>>>>>> <http://www.ncl.ucar.edu/Document/Functions/Built-in/fft2df.shtml>
>>>>>>>>>>> <http://goog_952811495>*
>>>>>>>>>>>
>>>>>>>>>>> *http://www.ncl.ucar.edu/Document/Functions/Built-in/fft2db.shtml*
>>>>>>>>>>> <http://www.ncl.ucar.edu/Document/Functions/Built-in/fft2db.shtml>
>>>>>>>>>>>
>>>>>>>>>>> You will have to loop over each time step.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> On Fri, Feb 22, 2019 at 12:09 AM Soma Roy <somaroy892 at gmail.com>
>>>>>>>>>>> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Hello,
>>>>>>>>>>>> I have a time series data (ntime, nlat, nlon) in spatial
>>>>>>>>>>>> domain. I want to calculate fourier decomposition of the same over lat lon.
>>>>>>>>>>>> How to do it using ncl? Is there any function available for the
>>>>>>>>>>>> above?
>>>>>>>>>>>>
>>>>>>>>>>>> Kindly inform.
>>>>>>>>>>>>
>>>>>>>>>>>> Thank you,
>>>>>>>>>>>> Soma
>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>> ncl-talk mailing list
>>>>>>>>>>>> ncl-talk at ucar.edu
>>>>>>>>>>>> List instructions, subscriber options, unsubscribe:
>>>>>>>>>>>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>>>>>>>>>>>
>>>>>>>>>>> _______________________________________________
>>>>>>> ncl-talk mailing list
>>>>>>> ncl-talk at ucar.edu
>>>>>>> List instructions, subscriber options, unsubscribe:
>>>>>>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>>>>>>
>>>>>> _______________________________________________
>>>>>> ncl-talk mailing list
>>>>>> ncl-talk at ucar.edu
>>>>>> List instructions, subscriber options, unsubscribe:
>>>>>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>>>>>
>>>>> _______________________________________________
>>>> ncl-talk mailing list
>>>> ncl-talk at ucar.edu
>>>> List instructions, subscriber options, unsubscribe:
>>>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>>>
>>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.ucar.edu/pipermail/ncl-talk/attachments/20190226/be07718b/attachment.html>
More information about the ncl-talk
mailing list