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From: kk KKsingh on 4 Mar 2010 03:43
Is there any code available which i can study ! where signal is reconstructed in frequency domain using Least sqaure...Like one of file submisson was Fast gridding method.....they calculate the frequency domain spectrum or i should say that they calculated A^(H)WY (which is dft with weights) now i want to apply least square on this ..fr reconstruction so that i can apply ifft and get back my signal..

Any help

kk
From: Rune Allnor on 4 Mar 2010 05:12
On 4 Mar, 09:43, "kk KKsingh" <akikumar1...(a)gmail.com> wrote:
> Is there any code available which i can study ! where signal is reconstructed in frequency domain using Least sqaure...Like one of file submisson was Fast gridding method.....they calculate the frequency domain spectrum or i should say that they calculated A^(H)WY (which is dft with weights) now i want to apply least square on this ..fr reconstruction so that i can apply ifft and get back my signal..

If you want your oiginal signal back, don't do anytrhing to it
in frequency domain:

y = ifft(fft(x));
max(abs(x-y)) == eps;

if one disregards numerical round-off errors.

Do anything at all to your signal in frequency domain, and you
will not get back the original signal. You might get back *a*
time-domain signal, but it will be a different signal than
the one you started out with.

Rune
From: kk KKsingh on 4 Mar 2010 05:24

But the files like
http://www.mathworks.com/matlabcentral/fileexchange/25135-nufft-nfft-usfft

calculates the approximate fourier spectrum now key to come back in the time domain is to do least sqaure reconstruction of this spectrum and get the corrected spectra and finally...fft and we r back in time domain on regular grid

For example purpose i can take dft for irregular samples which will give us approximate spectrum.........the files above can just replace the dft but that is not a issue ! issue is how to get the regular grid time domain signal back from dft spectrum


kk


Rune Allnor <allnor(a)tele.ntnu.no> wrote in message <9bc78e6f-443c-4b3c-979e-25ae8bba5745(a)g11g2000yqe.googlegroups.com>...
> On 4 Mar, 09:43, "kk KKsingh" <akikumar1...(a)gmail.com> wrote:
> > Is there any code available which i can study ! where signal is reconstructed in frequency domain using Least sqaure...Like one of file submisson was Fast gridding method.....they calculate the frequency domain spectrum or i should say that they calculated A^(H)WY (which is dft with weights) now i want to apply least square on this ..fr reconstruction so that i can apply ifft and get back my signal..
>
> If you want your oiginal signal back, don't do anytrhing to it
> in frequency domain:
>
> y = ifft(fft(x));
> max(abs(x-y)) == eps;
>
> if one disregards numerical round-off errors.
>
> Do anything at all to your signal in frequency domain, and you
> will not get back the original signal. You might get back *a*
> time-domain signal, but it will be a different signal than
> the one you started out with.
>
> Rune
From: Rune Allnor on 4 Mar 2010 05:43
On 4 Mar, 11:24, "kk KKsingh" <akikumar1...(a)gmail.com> wrote:
> But the files likehttp://www.mathworks.com/matlabcentral/fileexchange/25135-nufft-nfft-...
>
> calculates the approximate fourier spectrum now key to come back in the time domain is to do least sqaure reconstruction of this spectrum and get the corrected spectra and finally...fft and we r back in time domain on regular grid
>
> For example purpose i can take dft for irregular samples which will give us approximate spectrum.........the files above can just replace the dft but that is not a issue ! issue is how to get the regular grid time domain signal back from dft spectrum

If you have questions about files you found on the file
exchange, ask the authors of those fles.

Rune
From: kk KKsingh on 4 Mar 2010 06:09
Sir,

My question is a general one not with the author of the file.

KK


Rune Allnor <allnor(a)tele.ntnu.no> wrote in message <4058b34d-2feb-46b6-b992-0ce110a65b8f(a)y17g2000yqd.googlegroups.com>...
> On 4 Mar, 11:24, "kk KKsingh" <akikumar1...(a)gmail.com> wrote:
> > But the files likehttp://www.mathworks.com/matlabcentral/fileexchange/25135-nufft-nfft-...
> >
> > calculates the approximate fourier spectrum now key to come back in the time domain is to do least sqaure reconstruction of this spectrum and get the corrected spectra and finally...fft and we r back in time domain on regular grid
> >
> > For example purpose i can take dft for irregular samples which will give us approximate spectrum.........the files above can just replace the dft but that is not a issue ! issue is how to get the regular grid time domain signal back from dft spectrum
>
> If you have questions about files you found on the file
> exchange, ask the authors of those fles.
>
> Rune
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