🚀 go-pugleaf

I'm trying to understand the output of RFFTF (of Swarztrauber's
FFTPACK from netlib) so that I can plot a pretty frequency
spectrum with gnuplot to go with my time domain data. I don't
pretend to understand FFTs too well.  The relevant lines of
fft.doc are appended. Would someone expend a few minutes
sending me email? Thank you.

BTW, 
     [1] has FFTPACK been f2c'ed and stored somewhere (some systems
don't come with FORTRAN compilers, and yes I am aware of NR, but
alas it cannot be redistributed freely)?
     [2] is there a better newsgroup to bother about how to
actually *use* FFTs in case I get confused by books?

--mccauley@ecn.purdue.edu

from fft.doc of netlib's fftpack (except I changed 'l' to 'el'
for readability):
> r       r(1) = the sum from i=1 to i=n of r(i)
> 
>         if n is even set el =n/2   , if n is odd set el = (n+1)/2
> 
>           then for k = 2,...,el
> 
>              r(2*k-2) = the sum from i = 1 to i = n of
> 
>                   r(i)*cos((k-1)*(i-1)*2*pi/n)
> 
>              r(2*k-1) = the sum from i = 1 to i = n of
> 
>                  -r(i)*sin((k-1)*(i-1)*2*pi/n)
>
>         if n is even
> 
>              r(n) = the sum from i = 1 to i = n of
> 
>                   (-1)**(i-1)*r(i)