FFTW 3.1.2 - fftw_plan_many_dft

Hello guys,

I wanted to ask something concerning FFTW 3.1.2
I want to compute a 2D Fourier Transform of a 64x64 array. For research
reasons I need to calculate firstly 64 transforms, thus the rows, and then
in order to transpose between the two dimensions I NEED to use the strided
calls to check their performance. This is what I do:

FOR the x dimension
-------------------

fftw_plan_many_dft(rank, n, howmany, input, inembed=NULL, istride, idist,

	output, onembed, ostride=NULL, odist, FFTW_FORWARD, FFTW_MEASURE);

where rank=1, n[0]=64, howmany=64, istride=ostride=1, idist=odist=64

and to compute the 2nd dimension I pass as an input the output from above

FOR the y dimension
-------------------

fftw_plan_many_dft(rank, n, howmany, output, inembed=NULL, istride2,
idist2, final, onembed=NULL, ostride2, odist2, FFTW_FORWARD,
FFTW_MEASURE);

where rank=1, n[0]=64, howmany=64, istride2=ostride2=64, idist2=odist2=1

Any ideas why am I getting this all wrong? From my tests I thing that the
wrong arguments are those concerning the stride and dist but they seem
correct... Please help

Thank you in advance

I think the better and faster approach will be to use fft2 function
available in octave. Octave is a free equivalent of matlab and can
be installed on windows and linux machines.

y = fft2(a, m, n);

Regards
Bharat Pathak

Arithos Designs
www.Arithos.com

DSP Design Consultancy and Training Company.

"bharat pathak" <bharat@arithos.com> wrote in message 
news:qY-dnW3XBLSVea3VnZ2dnUVZ_hOdnZ2d@giganews.com...
>I think the better and faster approach will be to use fft2 
>function
> available in octave. Octave is a free equivalent of matlab 
> and can

> be installed on windows and linux machines.
     ^^^^^^^^^^^^^^^^^^^^

Only if you first install Cygwin.  For this reason, Octave is a 
big disappointment and is in no way a replacement for Matlab 
(or FFTW).

On May 18, 9:41 pm, "solonas13" <solona...@hotmail.com> wrote:
> Hello guys,
>
> I wanted to ask something concerning FFTW 3.1.2
> I want to compute a 2D Fourier Transform of a 64x64 array. For research
> reasons I need to calculate firstly 64 transforms, thus the rows, and then
> in order to transpose between the two dimensions I NEED to use the strided
> calls to check their performance. This is what I do:
>
> FOR the x dimension
> -------------------
>
> fftw_plan_many_dft(rank, n, howmany, input, inembed=NULL, istride, idist,
>
>         output, onembed, ostride=NULL, odist, FFTW_FORWARD, FFTW_MEASURE);
>
> where rank=1, n[0]=64, howmany=64, istride=ostride=1, idist=odist=64
>
> and to compute the 2nd dimension I pass as an input the output from above
>
> FOR the y dimension
> -------------------
>
> fftw_plan_many_dft(rank, n, howmany, output, inembed=NULL, istride2,
> idist2, final, onembed=NULL, ostride2, odist2, FFTW_FORWARD,
> FFTW_MEASURE);
>
> where rank=1, n[0]=64, howmany=64, istride2=ostride2=64, idist2=odist2=1
>
> Any ideas why am I getting this all wrong? From my tests I thing that the
> wrong arguments are those concerning the stride and dist but they seem
> correct... Please help
>
> Thank you in advance

The question that came to my mind is: why not just use FFTW's built-in
2-D transform functionality? It's easier to use than the advanced
interface you're working with. At one point I did understand the
meaning of all of the arguments (I think the documentation is a bit
terse on that topic), but my memory fails me now, so I'm not sure what
you might have wrong.

fftw_plan fftw_plan_dft_2d(int nx, int ny,
    fftw_complex *in, fftw_complex *out,
    int sign, unsigned flags);

Jason

>Only if you first install Cygwin.  For this reason, Octave is a 
>big disappointment and is in no way a replacement for Matlab 
>(or FFTW).

They have octave-forge version which does not require cygwin.
I have it running on XP machine. Cygwin not needed.