frequency analysis without numpy

debug domelectric at gmail.com
Thu Jan 22 02:12:44 CET 2009


On Jan 21, 11:31 am, sturlamolden <sturlamol... at yahoo.no> wrote:
> On Jan 21, 12:13 am, sturlamolden <sturlamol... at yahoo.no> wrote:
>
> > Apart from that, an FFT in pure python is going to be atrociously slow
> > for anything but the shortest signals. I cannot imagine why you want
> > to do this.
>
> Just to elaborate on this:
>
> The whole purpose of using FFT is speed. That pretty much excludes the
> use of Python.
>
> If you don't care about speed, you could just as well compute the DFT
> directly. The FFT is just a O(n lon n) algorithm for computing the
> DFT. Here is a DFT with O(N**2) behavior:
>
> from math import sin, cos, pi
>
> def real_dft(x):
>    ''' DFT for a real valued sequence x '''
>    r = []
>    N = len(x)
>    M = N//2 + 1 if N%2 else N//2
>    for n in range(M):
>       s = 0j
>       for k in range(N):
>          tmp = 2*pi*k*n/N
>          s += x[k] * (cos(tmp) - 1j*sin(tmp))
>       r.append(s)
>    return r
>
> S.M.

Thanks for the quick reply, so what do I pass the real_dft function
(obviously a list) but do I pass it the unpacked binary data?

Dom



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