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<div class="moz-forward-container"><font face="Courier New, Courier,
monospace">Dear All,<br>
</font><br>
<span style="font-family:"Courier New"">In the help
information for the FFT function I find that, regarding the
"inverse" FFT, fft(x,1), the formula is<br>
<br>
n<br>
x(k) = SUM(a(m)*exp(2*%i*%pi*(m-1)*(k-1)/n)<br>
m=1 <br>
<br>
But this is not the inverse FFT since it lacks the required 1/n
factor; however, fft(fft(a,-1),1) indeed returns a. So the
procedure seems to be mistakenly described in the help
information. <br>
<br>
Interestingly, the fftw3 documentation, <a
moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://www.fftw.org/fftw3.pdf"><a class="moz-txt-link-freetext" href="http://www.fftw.org/fftw3.pdf">http://www.fftw.org/fftw3.pdf</a></a>,
gives, on page 42, the same formula but it indicates it is an
unnormalized transform.<br>
<br>
Would you please clarify?<br>
<br>
Regards,<br>
<br>
Federico Miyara</span><o:p></o:p>
<div id="DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2">
<p class="MsoNormal"><o:p> </o:p></p>
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