[Numpy-discussion] Fast sizes for FFT

[Robert McGibbon]

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?

-Robert
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