[Scilab-users] circshift() : Scilab Enhancement Proposal

[Samuel Gougeon]

Hello Rafael,

Le 07/06/2018 à 15:04, Rafael Guerra a écrit :
>
> Hi Samuel,
>
> Fyi, many DFT references recommend averaging the values at endpoints 
> and discontinuities in general. See for instance:
>
> Briggs, W. L. and V. E. Henson [1005] The DFT: an owner's manual for 
> the Discrete Fourier Transform, SIAM, Philadelphia.
>

 >and discontinuities in general

Yes, that's a point. If a specific processing is used for the edges, it 
would look strange to not implement it as well in the body of the 
initial signal. From here, a criteria (and likely some threshold) must 
be set to decide what's a discontinuity, and what's not.
I did not go into any reading -- and frankly, if there is a summarized 
performances comparison and a standard published procedure --, it would 
be easier just to implement it, instead of reinventing the wheel with 
external tests. Then, i am afraid that it will come either with some 
choices with respect to the type of input signal, or with a bunch of 
processing options (making circshift a signal processing function rather 
than just a general matrix handling operation).

Anyway, no damping window could process inner discontinuities.

To me, the main advantage of the DFT was to avoid local interpolations, 
in order to stay simple.
If the algo then implements some interpolations, why not performing the 
fractional part of the shift
only by interpolation, instead of /in addition/ to the DFT?
If you can provide some quantified rationale and possibly some finalized 
algo, it would be fine.

Best regards
Samuel

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