Drexel dragonThe Math ForumDonate to the Math Forum



Search All of the Math Forum:

Views expressed in these public forums are not endorsed by Drexel University or The Math Forum.


Math Forum » Discussions » Software » comp.soft-sys.matlab

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

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]
Nasser Abbasi

Posts: 5,597
Registered: 2/7/05
Re: spectral derivation of aperiodic function
Posted: Feb 11, 2013 5:37 PM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

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



Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© Drexel University 1994-2014. All Rights Reserved.
The Math Forum is a research and educational enterprise of the Drexel University School of Education.