[SciPy-Dev] fftpack.convolve.convolve

Eric Moore ewm@redtetrahedron....
Wed Aug 21 10:50:34 CDT 2013


Clemens Novak wrote:
> Hi,
>
> I've been working on extending the fftpack tutorial page (you can see
> the current status here:
> https://github.com/ClemensFMN/scipy/blob/tut_fft/doc/source/tutorial/fftpack.rst
> ) and I stumbled across the function fftpack.convolve.convolve .
>
> Sorry the blunt question, but what does this function do? From the name
> I'd assume that it calculates the convolution of two sequences (as
> convolve in scipy.signal does) using the fft (since it is part of
> fftpack), but appearently it doesn't:
>
> import numpy as np
> import scipy.fftpack.convolve as conv
> import scipy as sp
> import scipy.signal as sig
>
>
> x = np.array([1.0, 0.0, 0.0])
> h = np.array([1.0, 2.0, 3.0])
>
> y1 = conv.convolve(x, h)
> [ 5. -1. -1.]
>
> y2 = sig.convolve(x, h)
> [ 1.  2.  3.  0.  0.]
>
> y3 = sp.ifft(sp.fft(x) * sp.fft(h))
> [ 1.+0.j  2.+0.j  3.+0.j]
>
> Does the function extend its first and/or second argument to a periodic
> sequence and perform then the convolution (I tried some ideas but that
> didn'twork either)? It would be great if someone could please provide
> some insight...
>
> Regards - Clemens
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AFAICT, fftpack.convolve exists in support of pseudo_diffs.py.  Look 
there to see some examples.

-Eric



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