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[Tftb-help] Newbie, want to perform a (probably) very simple task


From: Thomas Baruchel
Subject: [Tftb-help] Newbie, want to perform a (probably) very simple task
Date: Sat, 21 Oct 2006 15:21:25 +0200
User-agent: Mutt/1.4.2.1i

Hi,

after having looked a while on the net, I thought that TFTB was the right
tool for me. I installed Octave and TFTB, and the installation seems to be
all right. But I don't really know what I have to do for performing
something that looks a little like the Example 2 on the site:
  http://gdr-isis.org/tftb/tutorial/node8.html
Here is my problem. I have an arithmetical integer sequence in which
I suspected to be some periodical information. At a low level (C and fortran)
I performed some classical DFT manipulations and found a nice spectrum where
significant information is at some very precise easy to recognize
rational frequencies (like .33333333... or .20000000 or .199999999).
But obviously the signal isn't constant in the "time": frenquencies are
constant, but coefficients of the DFT become greater with "time".
What I want is to make some decomposition of each frequency in order
to see what my sequence is made with.
Thus I launched octave and typed what is on the web page above.
Since this web page tells what to type for the two initial steps, I did
it and saw exactly what was expected (I only had to change the value
concerning the size of the discrete sequence). The plot for the spectrum,
as expected, shows very well my various interesting frequencies. But
I really don't understand what I have to type for using and plotting
the analysis (in the web page, it is with tfrpwv byt maybe another
algorithm would be also good).

Precisions, my sequence has a length 65536;
only integers are in it.
For instance I want to study frequency corresponding to 1/3.

Could someone help me to go further, then I think one I will have understood,
I will be able to do by myself. As I told it, I am also a newbie at
Matlab/Octave...

Regards,

-- 
Thomas Baruchel




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