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 Post subject: looking for autocorrelation routine
PostPosted: Mon Jan 07, 2013 6:08 pm 
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I am looking for a pb autocorrelation routine.
I have a row of 400000 numbers, and i like to do an autocorrelation on it.
( For my SETI - program , just to find is there a system in the noise i do receive....)

I can find enough mathematics for it... but i can not transform that to a pb program.

Thanks Wim


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 Post subject: Re: looking for autocorrelation routine
PostPosted: Mon Jan 07, 2013 8:39 pm 
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Maybe using Wiener's method of auto correlation using an FFT / IFFT


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 Post subject: Re: looking for autocorrelation routine
PostPosted: Mon Jan 07, 2013 8:43 pm 
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http://www.purebasic.fr/english/viewtopic.php?f=7&t=50511

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 Post subject: Re: looking for autocorrelation routine
PostPosted: Mon Jan 07, 2013 9:33 pm 
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Idle: yes i do read information about FFT and IFFT, but there has to be something in
between.. but i do not understand what.... (i have routines for a FFT and an IFFT)


Ideasvacuum: Your tips give nothing about autocorrelation... (if i am right)
but there was something like rosettacode.org... that looks great. but nothing
about autocorrelation....


By the way: good to see you both again, and thanks for your help !!!!!!


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 Post subject: Re: looking for autocorrelation routine
PostPosted: Mon Jan 07, 2013 9:53 pm 
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idle, should it be as follows?

you do a FFT on the row of numbers.
You get then two rows of numbers... the reel part and the imaginair part. REX(i) and IMX(i)

if i do understand the wiener method i have to multiply the reel part with the imaginair part
This gives a new row of numbers.

Then i have to do an IFFT on that row of numbers....

Should this be it?????


.


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 Post subject: Re: looking for autocorrelation routine
PostPosted: Mon Jan 07, 2013 10:43 pm 
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Hi Wim -well essentially, autocorrelation is crudely based on statistics. Have a look at the subject on Wikipedia.

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 Post subject: Re: looking for autocorrelation routine
PostPosted: Mon Jan 07, 2013 10:50 pm 
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Yes, ideasVacuum,
i have looked at wikipedia, and lots of other sites.. but i can find only unreadable mathematical formules...

This is always my problem...

Wim


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 Post subject: Re: looking for autocorrelation routine
PostPosted: Mon Jan 07, 2013 11:39 pm 
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Well, this topic is not simple.
Here is an example lecture on convolution...
Once you know the theory, then comes the application in Digital Signal Processing or Statistics or Astronomy or whatever field you are pursuing. :wink:

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 Post subject: Re: looking for autocorrelation routine
PostPosted: Tue Jan 08, 2013 5:22 pm 
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Hi Skywalk,
It is a very nice lecture. Nice to follow, but convolution is not what i need.
A lecture about autocorrelation would be fantastic.

Wim


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 Post subject: Re: looking for autocorrelation routine
PostPosted: Tue Jan 08, 2013 5:45 pm 
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Hi wimapon,

Have you tried googling 'autocorrelation algorithm' ?

You might, perchance, find something there.

Regards

Dave

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 Post subject: Re: looking for autocorrelation routine
PostPosted: Tue Jan 08, 2013 6:33 pm 
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Yes Davido, i did that.
I come everytime on the same things.... or unreadable formulas of using of mathlab....

Wim


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 Post subject: Re: looking for autocorrelation routine
PostPosted: Tue Jan 08, 2013 7:07 pm 
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Numerical Recipes has code to do autocorrelation, it's available in Fortran, C and Pascal.


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 Post subject: Re: looking for autocorrelation routine
PostPosted: Tue Jan 08, 2013 10:57 pm 
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jack, ik heb ze gevonden, maar ik kan er niets mee......
ik kan de codes niet naar basic overschrijven...
jammer


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