[SciPy-User] rfft

[Charles R Harris]

On Mon, Jun 20, 2011 at 10:35 AM, garyr <garyr at fidalgo.net> wrote:

>
> ----- Original Message ----- From: "Charles R Harris" <
> charlesr.harris at gmail.com>
> To: "SciPy Users List" <scipy-user at scipy.org>
> Sent: Monday, June 20, 2011 8:11 AM
> Subject: Re: [SciPy-User] rfft
>
>
>
>  On Mon, Jun 20, 2011 at 9:03 AM, garyr <garyr at fidalgo.net> wrote:
>>
>>  If I generate a sine wave of a particular frequency in an array of type
>>> float32 or float64 and compute the transform using the function fft (in
>>> scipy/fftpack/basic.py) I find the signal in the correct bin. If I use
>>> the
>>> function rfft, which is described as returning the Fourier transform of a
>>> real sequence,  I find the signal in the bin corresponding to twice the
>>> actual frequency. I thought rfft would be the proper function to use for
>>> real (non-complex) data. What is the correct usage of rfft?
>>>
>>>
>>>  Could you provide an example?
>>
>> Chuck
>>
>>
>
>
Ah, rfft from scipy returns a *real* array with the complex numbers packed
in there together. That's why you can do it in place, the zero imaginary
parts for DC and Nyquist are omitted. If you want a convenient format, use
rfft from numpy.

Chuck
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