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From: Fatemeh on 5 Jul 2008 05:24
Dear all;

I'm going to use rlft3.f (3D Fast Fourier transform subroutine in
Numerical Recipes book )
I have constructed a 107*107*107 mesh for data.
I should call rlft3(data,speg,nn1,nn2,nn3,isign).
-----------------------------------------------------------------------------
SUBROUTINE rlft3(data,speq,nn1,nn2,nn3,isign)
INTEGER isign,nn1,nn2,nn3
COMPLEX data(nn1/2,nn2,nn3),speq(nn2,nn3)
-----------------------------------------------------------------------------
1- I don't understand why for data is written nn1/2 ? I have a
107*107*107 mesh!!!
2- Is it true to put nn1=nn2=nn3=107
3- I don't know what should I put instead of speq ?

I'm anxiously looking forward your reply and guidlines.
With my best regards,
Fatemeh
From: dominiq on 5 Jul 2008 05:41
On 5 juil, 11:24, Fatemeh <fateme.mirj...(a)gmail.com> wrote:
> Dear all;
>
> I'm going to use rlft3.f (3D Fast Fourier transform subroutine in
> Numerical Recipes book )
> I have constructed a 107*107*107 mesh for data.
> I should  call rlft3(data,speg,nn1,nn2,nn3,isign).
> --------------------------------------------------------------------------- --
>      SUBROUTINE rlft3(data,speq,nn1,nn2,nn3,isign)
>       INTEGER isign,nn1,nn2,nn3
>       COMPLEX data(nn1/2,nn2,nn3),speq(nn2,nn3)
> --------------------------------------------------------------------------- --
> 1- I don't understand why for data is written nn1/2 ? I have a
> 107*107*107 mesh!!!
> 2- Is it true to put nn1=nn2=nn3=107
> 3- I don't know what should I put instead of speq ?
>
> I'm anxiously looking forward your reply and guidlines.
> With my best regards,
> Fatemeh

The basic FFT requires sizes that are powers of 2. Some packages
extend that to powers of small primes (typically 3 and 5), but I don't
think this is the case for Numerical Recipes. Nevertheless 107 is a
prime and is unlikely to be accepted in any FFT package.

As a general advice RTFM before using any package!

Dominique

From: Fatemeh on 5 Jul 2008 06:36
On Jul 5, 1:41 pm, dominiq <domi...(a)lps.ens.fr> wrote:
> On 5 juil, 11:24, Fatemeh <fateme.mirj...(a)gmail.com> wrote:
>
>
>
> > Dear all;
>
> > I'm going to use rlft3.f (3D Fast Fourier transform subroutine in
> > Numerical Recipes book )
> > I have constructed a 107*107*107 mesh for data.
> > I should call rlft3(data,speg,nn1,nn2,nn3,isign).
> > --------------------------------------------------------------------------- --
> > SUBROUTINE rlft3(data,speq,nn1,nn2,nn3,isign)
> > INTEGER isign,nn1,nn2,nn3
> > COMPLEX data(nn1/2,nn2,nn3),speq(nn2,nn3)
> > --------------------------------------------------------------------------- --
> > 1- I don't understand why for data is written nn1/2 ? I have a
> > 107*107*107 mesh!!!
> > 2- Is it true to put nn1=nn2=nn3=107
> > 3- I don't know what should I put instead of speq ?
>
> > I'm anxiously looking forward your reply and guidlines.
> > With my best regards,
> > Fatemeh
>
> The basic FFT requires sizes that are powers of 2. Some packages
> extend that to powers of small primes (typically 3 and 5), but I don't
> think this is the case for Numerical Recipes. Nevertheless 107 is a
> prime and is unlikely to be accepted in any FFT package.
>
> As a general advice RTFM before using any package!
>
> Dominique
Thanks for your guidelines.
if I choose a size that is power of 2, about my another questions is
there anyone that has some suggestion?
From: dominiq on 5 Jul 2008 08:00
On 5 juil, 12:36, Fatemeh <fateme.mirj...(a)gmail.com> wrote:
> On Jul 5, 1:41 pm, dominiq <domi...(a)lps.ens.fr> wrote:
>
> > On 5 juil, 11:24, Fatemeh <fateme.mirj...(a)gmail.com> wrote:
>
> > > Dear all;
>
> > > I'm going to use rlft3.f (3D Fast Fourier transform subroutine in
> > > Numerical Recipes book )
> > > I have constructed a 107*107*107 mesh for data.
> > > I should  call rlft3(data,speg,nn1,nn2,nn3,isign).
> > > --------------------------------------------------------------------------- --
> > >      SUBROUTINE rlft3(data,speq,nn1,nn2,nn3,isign)
> > >       INTEGER isign,nn1,nn2,nn3
> > >       COMPLEX data(nn1/2,nn2,nn3),speq(nn2,nn3)
> > > --------------------------------------------------------------------------- --
> > > 1- I don't understand why for data is written nn1/2 ? I have a
> > > 107*107*107 mesh!!!
> > > 2- Is it true to put nn1=nn2=nn3=107
> > > 3- I don't know what should I put instead of speq ?
>
> > > I'm anxiously looking forward your reply and guidlines.
> > > With my best regards,
> > > Fatemeh
>
> > The basic FFT requires sizes that are powers of 2. Some packages
> > extend that to powers of small primes (typically 3 and 5), but I don't
> > think this is the case for Numerical Recipes. Nevertheless 107 is a
> > prime and is unlikely to be accepted in any FFT package.
>
> > As a general advice RTFM before using any package!
>
> > Dominique
>
> Thanks for your guidelines.
> if I choose a size that is power of 2, about my another questions is
> there anyone that has some suggestion?

Since the multi-dimensional FFT takes the FFT along each dimension,
each size has to be a power of 2. For the other questions read
Numerical Recipes to know how to use the subroutine (aka RTFM!-).

Dominique

From: James Van Buskirk on 5 Jul 2008 10:38
"dominiq" <dominiq(a)lps.ens.fr> wrote in message
news:7061d478-b8c5-4a07-ab4f-9acb9d95d350(a)l64g2000hse.googlegroups.com...

> The basic FFT requires sizes that are powers of 2. Some packages
> extend that to powers of small primes (typically 3 and 5), but I don't
> think this is the case for Numerical Recipes. Nevertheless 107 is a
> prime and is unlikely to be accepted in any FFT package.

107 is kind of ugly because (107-1)/2 = 53 which I do in fact have an
FFT for:

http://home.comcast.net/~kmbtib/codelets.ZIP

but 53 is rather ugly in itself. For some of these primes it gets
more efficient to use the chirp-z method rather than Rader's method,
but you can do an FFT of any order if you really have to.

--
write(*,*) transfer((/17.392111325966148d0,6.5794487871554595D-85, &
6.0134700243160014d-154/),(/'x'/)); end


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