[Numpy-discussion] Fast sizes for FFT

Charles R Harris charlesr.harris at gmail.com
Tue Dec 23 21:47:07 EST 2014

On Tue, Dec 23, 2014 at 7:32 PM, Robert McGibbon <rmcgibbo at gmail.com> wrote:

> Hey,
> The performance of fftpack depends very strongly on the array size --
> sizes that are powers of two are good, but also powers of three, five and
> seven, or numbers whose only prime factors are from (2,3,5,7). For problems
> that can use padding, rounding up the size (using np.fft.fft(x,
> n=size_with_padding)) to one of these multiples makes a big difference.
> Some other packages expose a function for calculating the next fast size,
> e.g: http://ltfat.sourceforge.net/notes/ltfatnote017.pdf.
> Is there anything like this in numpy/scipy? If not, would this be a
> reasonable feature to add?
It would be nice to have, but an integrated system would combine it with
padding and windowing. Might be worth putting together a package, somewhat
like seaborn for plotting, that provides  a nicer interface to the fft
module. Tracking downsampling/upsampling  and units would also be useful. I
don't know if anyone has done something like that already...

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