[SciPy-user] FFT speed ?

Scott Ransom sransom@nrao....
Wed Feb 7 10:12:36 CST 2007


On Wed, Feb 07, 2007 at 04:39:21PM +0200, Stefan van der Walt wrote:
> On Wed, Feb 07, 2007 at 03:18:19PM +0100, Samuel GARCIA wrote:
> > yes I was thinking of doing something like that but
> > fft(a,pow(2,18)).shape is of course 262144 (2**18)
> > and when I use ifft after that The length of my signal have changed I have an
> > interpolated signal ... new problem for me ...
> 
> An interpolated signal?

Padding a time series gives you an interpolated (actually, the
term often used is "oversampled" Fourier spectrum).

Scott

> In [19]: N.real(N.fft.ifft(N.fft.fft(N.arange(11),16)))
> Out[19]: 
> array([  0.,   1.,   2.,   3.,   4.,   5.,   6.,   7.,   8.,   9.,  10.,
>         -0.,   0.,   0.,   0.,   0.])
> 
> Padding in the Fourier-domain, on the other hand:
> 
> In [20]: N.real(N.fft.ifft(N.fft.fft(N.arange(11)),16))
> Out[20]: 
> array([ 0.        ,  2.10035464,  3.04455839,  1.35780382,  3.23688237,
>         3.12291155,  2.35790278,  4.12133152,  3.4375    ,  3.29213721,
>         5.00323313,  3.69035768,  4.32561763,  5.98165513,  3.3443057 ,
>         6.58344845])
> 
> 
> Cheers
> Stéfan
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Scott M. Ransom            Address:  NRAO
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