Confusion about 2D DFTs

On Aug 3, 9:17 am, Michel Rouzic <Michel0...@yahoo.fr> wrote:
> I should also probably mention that I'm implementing that using FFTW 3
> (no Matlab to toy around with), and that its documentation is pretty
> poor on the very topic of my problem. It seemingly doesn't tell what
> the output matches to depending on the transform. For example I
> noticed that the output is quite different between a 2D Discrete
> Hartley Transform and a 2D DFT (and also a 2D DCT, but I know why that
> one is different, I at least understand that, but the documentation
> won't say anything about it),

Note that the section "what FFTW really computes" of the manual gives
the exact formulas for the transforms that it performs.

However, as the introduction to the manual explains, the manual makes
no attempt to be a tutorial on the meaning and properties of the DFT.
There are plenty of textbooks on that. The manual assumes that you
know what DFT (or DCT, or ...) you want to compute and why, and its
only function is to tell you how to use FFTW to perform that
computation.

Regards,
Steven G. Johnson

On 5 Aug, 03:59, "Steven G. Johnson" <stev...@alum.mit.edu> wrote:

> However, as the introduction to the manual explains, the manual makes
> no attempt to be a tutorial on the meaning and properties of the DFT.
> There are plenty of textbooks on that. The manual assumes that you
> know what DFT (or DCT, or ...) you want to compute and why, and its
> only function is to tell you how to use FFTW to perform that
> computation.

The documentation of a technical library should not attempt
to be a tutorial. However, it might be useful for users if
the documentation provides pointers to good tutorials.

Rune

On Aug 5, 12:05 pm, Rune Allnor <all...@tele.ntnu.no> wrote:
> The documentation of a technical library should not attempt
> to be a tutorial. However, it might be useful for users if
> the documentation provides pointers to good tutorials.

It actually does provide a pointer to at least one good textbook on
applications of FFTs, and the links page lists many more resources
online.