[Numpy-discussion] chirp-z

[Charles R Harris]

On 5/27/07, Matthieu Brucher <matthieu.brucher at gmail.com> wrote:
>
> Hi,
>
> Isn't the chirp transform only two cross-correlations ? And for a fast
> one, there is a module in SciPy, and I think that kind of operation belongs
> more to Scipy than Numpy ;)


Umm, no,

There really aren't any transparent fast fft convolutions in SciPy. The
closest thing is in signaltools, fftconvolve, and if you ask it to convolve,
say, sequences whose length add up to 7902, then it will do a size 7901
transform. Because 7901 is prime this takes about 300 times as long as a
transform of size 8192. That glitch could be fixed, but I think something as
basic as fftconvolve should reside at a higher level than
scipy.signalsanyway, say in
numpy.fft.

There are other scipy functions that do convolution, but those that use an
fft are limited. There is a (buggy) version for 2d arrays in stsci, and a
version with limited (real) functionality in fftpack. I don't see any more.

Chuck
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