Re: [eigen] A complex FFT for Eigen
• To: eigen@xxxxxxxxxxxxxxxxxxx
• Subject: Re: [eigen] A complex FFT for Eigen
• From: "Benoit Jacob" <jacob.benoit.1@xxxxxxxxx>
• Date: Fri, 28 Nov 2008 03:16:21 +0100
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```2008/11/27 Matthias Pospiech <matthias.pospiech@xxxxxx>:
> Standard FFT can only use powers of 2, others are usual normal DFT routine
> which are much less optimized.

OK, I see.

> Fourier Transform is by definition using complex numbers.

As far as the math aspect is concerned -- I know ;)
My question was more, is it in practice used that way or is it somehow
hidden like e.g. with Fourier series when one splits off the cos and
sin parts of the fourier series that is basically a complex series
too.

> Very often people
> are using FFTs with matrixes. However usual FFT routines require plain C
> Arrays. That would require to copy the data from Eigen to C-Array, do
> Fourier Transform, copy back to Eigen matrix and such.

No, if you have a C implementation of FFT asking for a plain C array,
you can just pass to it the data pointer of your Eigen matrix, as
returned by data(), it is like a plain C array.

> Thats my
> understanding why it could make sence to have an optimzed FFT routine which
> can directly use eigen matrices.

And so, I'm still undetermined whether it makes sense to include FFT in Eigen.

Cheers,
Benoit

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```

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