[SciPy-user] FFT speed ?

Anne Archibald peridot.faceted@gmail....
Wed Feb 7 11:13:12 CST 2007

On 07/02/07, Samuel GARCIA <sgarcia@olfac.univ-lyon1.fr> wrote:
>  Yes I know this.
>  But 186888 186889 and 186890 are not power of 2 and the computation time is
> very very different just for a difference of size of only one point.
>  What is the reason ?
>  And how to deal with that ? (I realy need to compute fft with a random
> nomber of point)

Many problems can be solved by padding. But once in a while one comes
up which needs a particular number of points, and it's not always a
power of two.

Can FFTW (or any of the FFT packages numpy/scipy can use) compute an
FFT of size 186889 in a reasonable time? I know there are algorithms
for large prime factors, and for small prime factors, and that you can
combine the two (though perhaps primes of moderate size are a

Anne M. Archibald

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