[SciPy-User] fast autocorrelation

[Neal Becker]

Pierre Barbier de Reuille wrote:

> scipy.fftpack has two functions for that: rfft and irfft. They are both
> faster than fft/ifft, so maybe you want to use that? Or is it still too
> slow?
> 

I believe irfft will do complex->real (just as rfft does real->complex).

In this case, we have frequency domain values, but they are pure real.  So
we want ifft from real->complex.