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From: dbd <dbd@ieee.org>
Newsgroups: comp.soft-sys.matlab
Subject: Re: About FFT and Even Function
Date: Sat, 31 Oct 2009 22:56:41 -0700 (PDT)
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On Oct 31, 10:42 pm, "Oscar " <oscarodrig...@yahoo.es> wrote:
> Hello everyone,
>
> I have a doubt about FFT function on Matlab. I know when I have an even and real function its FFT give only real values. But, when I calculate, for  example, the FFT of a cosine function result real and imaginary values. I think I making a mistake on my interpretation of this result. Anyone can help me please :)
>
> Thanks and sorry for my english!!!

There are often mistakes made confusing 'symmetry' with 'fft-
evenness'. For examples, compare the difference between Matlab's
'symmetric' and 'periodic' forms of window functions. Use the windows
as the real signals to be transformed.

A good reference is fred harris' paper on windows. Look at the first
column of page 173. The paper is available a number of places. One is:

http://www.utdallas.edu/~cpb021000/EE%204361/Great%20DSP%20Papers/Harris%20on%20Windows.pdf

Dale B. Dalrymple