# Help me with cross correlation, please.

Started by September 13, 2010
```Hi!

I'm porting a little Matlab function in C language. My problems raise with
xcorr() function. I need to calculate raw correlation (without
normalization) between two vectors. I've found this code
http://local.wasp.uwa.edu.au/~pbourke/miscellaneous/correlate/ , but it
calculates only a normalized correlation coefficient. However, I've tried
to adjust it to calculate a raw correlation vector, but results are wrongs
(compared with Matlab). I've also made other trials (i.e. using
convolution), but all without success. I don't know what can I do. Isn't
there xcorr() source code?

P.S. : I'm completely newbie on DSP and signal theory
P.S.2: I need to calculate xcorr() without FFT (for the moment)

If you need any source code, ask for it.

```
```On Sep 13, 8:36&#2013266080;am, "Manugal" <manugal83@n_o_s_p_a_m.yahoo.it> wrote:
> Hi!
>
> I'm porting a little Matlab function in C language. My problems raise with
> xcorr() function. I need to calculate raw correlation (without
> normalization) between two vectors. I've found this codehttp://local.wasp.uwa.edu.au/~pbourke/miscellaneous/correlate/, but it
> calculates only a normalized correlation coefficient. However, I've tried
> to adjust it to calculate a raw correlation vector, but results are wrongs
> (compared with Matlab). I've also made other trials (i.e. using
> convolution), but all without success. I don't know what can I do. Isn't
> there xcorr() source code?
>
> P.S. : I'm completely newbie on DSP and signal theory
> P.S.2: I need to calculate xcorr() without FFT (for the moment)
>
> If you need any source code, ask for it.

I don't do Matlab, but maybe these will help:

definition and example of non-normalized cross-correlation:

http://www.scribd.com/doc/25334405/The-Discrete-Fourier-Transform-Part-6-Cross-Correlation

I think the above is so long that it might wrap-around.  If so, just
concatenate the following:

http://www.scribd.com/doc/25334405/
(and)
The-Discrete-Fourier-Transform-Part-6-Cross-Correlation

There's also these for Matlab xcorr( ):

http://www.mathworks.com/help/toolbox/signal/xcorr.html

http://www.dsprelated.com/groups/matlab/show/3926.php

Kevin McGee
```