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From: "Nasser M. Abbasi" <nma@12000.org>
Newsgroups: comp.soft-sys.matlab
References: <hcj73a$b5$1@fred.mathworks.com>
Subject: Re: About FFT and Even Function
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Date: Sun, 1 Nov 2009 01:11:25 -0600
Xref: news.mathworks.com comp.soft-sys.matlab:581569



"Oscar " <oscarodrigo3k@yahoo.es> wrote in message 
news:hcj73a$b5$1@fred.mathworks.com...
> 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!!!

If the data sequence itself is real and even (i.e. x[n]=x[N-n]) where N is 
the sample points, then the discrete fourier transform (which fft is an 
implementation of) should result in all real values.  i.e. g[k] for k=1..N 
should be real values.

Is this the case with your sampled data?

--Nasser