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Topic: spectral derivation of aperiodic function
Replies: 2   Last Post: Feb 11, 2013 5:37 PM

 Messages: [ Previous | Next ]
 Nasser Abbasi Posts: 6,677 Registered: 2/7/05
Re: spectral derivation of aperiodic function
Posted: Feb 11, 2013 5:37 PM

On 2/11/2013 3:51 PM, TideMan wrote:

>>
>>

>>> I wonder if there exist other spectral methods
>>
>>> to calculate the derivative on an aperiodic domain or if my only hope is
>>
>>> to use the finite difference method?
>>
>>
>>
>> no, it's likely your 'other hope' is to spend some time thinking more carefully about your problem(s).

>

> Yes, I was bemused by this post also.
> It implies that Kolmogorov's -5/3 law of turbulence and all other such work is rubbish.
> Perhaps OP is confusing non-periodic with non-stationary?
> FFT is not good for non-stationary data.
>

Actually, what I was confused about is not that saying that
FFT can't be used for aperiodic signals, but the need to use
FFT to find derivatives.

At school the teacher did not talk about this part of FFT.
He just told us FFT is used to find frequencies on signals.

I mean, if one wants to find derivative of a discrete
sequence in Matlab, why not use the command diff() ?

http://www.mathworks.com/help/matlab/ref/diff.html

or 3 points centered difference, or such schemes.

So I think there is still more to this issue than meets
the eyes.

--Nasser

Date Subject Author
2/11/13 Derek Goring
2/11/13 Nasser Abbasi