Re: [Discuss-gnuradio] a crazy problem with GNURadio fft

[Mostafa Alizadeh]

Excuse me all! 

That was my fault because previously I checked the FFTW with Matlab I did know its difference as Murcus mentioned. However, I suddenly suspect the FFTW again! 

 Thank you so much 

On Tue, Aug 26, 2014 at 6:31 PM, Marcus Müller <address@hidden> wrote:

Thanks Sylvain,
not finding that drove me crazy (more crazy than usual); the zeroth
element must be sum(range(fftlen))=(63+0)*(64/2) = 63*32 = 2048 - 32 =
2016, like in the matlab result, yet I did not find where the data
stopped flowing... now,
sum(range(fftlen/sizeof(gr_complex)))=sum(range(8))=(7+0)*8/2=28
explains that :)

Also, Mostafa, you call your transform ifft, yet you set forward=true,
which might be a bit confusing in the future.
For the IFFT, Matlab does something different than the pure FFTW that
GNU Radio uses: it divides by fft_size, compare [1] to [2].

Greetings,
Marcus

[1]http://www.mathworks.de/de/help/matlab/ref/fft.html
[2]http://www.fftw.org/doc/The-1d-Discrete-Fourier-Transform-_0028DFT_0029.html#The-1d-Discrete-Fourier-Transform-_0028DFT_0029

On 26.08.2014 15:36, Sylvain Munaut wrote:
>>     memcpy(ifft->get_inbuf(), in, fft_size);
> fft_size * sizeof(gr_complex)
>

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