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From: dbd <dbd@ieee.org>
Newsgroups: comp.soft-sys.matlab
Subject: Re: FFT,IFFT, and NDFT,NFFT
Date: Mon, 6 Jul 2009 15:42:11 -0700 (PDT)
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On Jul 6, 1:47 pm, "guj " <gulatiaks...@gmail.com> wrote:

>
> What are your comments on the code below:
> FFT is giving the same result as DFT for Non uniform sampling. I am curious to know the difference between NDFT and DFT ...Notation

>  CODE REMOVED

> So question is Which one is right for Non uniform sampling..

Neither

> Is matlab DFT formula (which i have taken from help) is same as FFT

Yes

> and can handle only fixed sample...

Yes

> what factor in DFT algorithm constraining it for fixed sampling.
>
> In DFT, algorithm we are multiplying our Coefficient with twiddle factor, that twiddle factor is equally spaced ...is that the constrain...
>

The FFT and the conventionally defined DFT it is equivalent to are
only defined for equispaced inputs and outputs when used to transform
from time to frequency domains. These functions follow the GIGO
principle. If you input anything else (Garbage In) , you will output
something else (Garbage Out)
.
> twiddle factor= exp(-2*pi*i*k*n/N)   ..IN this when we divide it by N, we only mean to normalise it..isnt it..also 2pi is my sampling frequency ...
>
> All these doubts are there because of the code which i have written above and i am dubious why its giving same result as fft
That is what it is defined to do.

> ..Also what FFT do when it incur a irregular sampling....although it give wrong result but what is its working on such kind of input

Remember GIGO!


Dale B. Dalrymple