NumPy and FFT

[Travis Oliphant]

> 
> P.S. More NumPy savvy folks can probably point out a much more
> efficient way of calculating the negative frequencies...
> 

I use this function all the time.  It gives me the frequencies of the
output of the FFT call:  I call it freqs (somebody please give me a better
name for it :-) )

def freqs(N,sample=1.0):
    """freq = freqs(N,sample=1.0)

    return the frequency bins in cycles/unit (with zero at the start) given a
    window length N and a sample spacing.
    """
    sample = float(sample)
    return concatenate((arange(0,(N+1)/2,1,'d'),arange(-(N-1)/2,0,1,'d')))/N/sample


Best,

Travis