Re: [Help-gsl] 2d FFTs, DCTs, etc.

[Dimitris Papavasiliou]

Brian Gough wrote:
> Hello,
>
> Thanks for your message.  
>
> The Mixed radix FFTs in GSL are a reimplementation of FFTPACK. The DCT
> and DST from FFTPACK were not implemented though due to lack of
> resources.  From my point of view, that would be the first priority to
> add to the existing ffts.
>   
Well I implemented the DCT (and just type II) myself, so it probably 
isn't what you're looking for.
>  > b) Is there a reason why there are no vector/matrix interfaces to the 
>  > fft functions (in constrast to the wavelets routines)?
>
> The normal GSL convention is that we don't duplicate array and vector
> functions as the vector functions are just a wrapper with v->data,
> v->stride, v->size arguments.  Some functions do have these, but it's
> historical.  A vector wrapper could be useful if people want that, but
> I'd like to keep it out of gsl itself as it means there are twice as
> many functions to maintain and test.
>   
It would be more logical to do it the other way round I think (that is 
implement just gsl_vector versions and let the user create a view of his 
arrays if needed) but it's the same thing I guess.  It also means that 
my wrappers won't be of much use (and I just finished the templates for 
double and float today, oh well).  Let me know if you're interested in 
any of them or the DCTs (although they'll need some work for the initial 
permutation).
>  > c) Is there a reason why there are no two-dimensional fft routines?  For 
>  > real data there would be the problem of computing them in-place I 
>  > suppose but for complex data computation is pretty simple using 
>  > row-column decomposition.
>
> At the time I wrote the FFTs I was looking for a good multidimensional
> solution.
>
> I did not find anything that was substantially better than the user
> calling the FFT on the rows and columns themselves, so I did not
> implement anything
Well as I've written in a previous message I've arrived at the same 
conclusion.

Dimitris P.