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 Post subject: real part of fft
PostPosted: Wed Aug 17, 2011 11:05 am 
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Joined: Wed Aug 17, 2011 10:56 am
Posts: 2
Hello,
I am new to Alglib, and i am trying to do an fft of the joint positions recieved via Kinect sensor.
For each joint i am trying to make 3 FFT of 1 dimension. ( I know it would be better 1 of 3, but i don't see the point for now, so i rather KISS)

I was searching for an fft c# library which would simple enough for me to use, Alglib seems very simple

Unfortunately, i can not manage to find a simple way to convert the string fft out in an array of only the real part. I know it seems stupid but because of the +/- and i's, i can only find buggy ways.

I get to the array of complex numbers in string format, and i then mess everything.

Thank you for your help

Samba

PS: Rather than buying the commercial part, are small donations via paypal possible?


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 Post subject: Re: real part of fft
PostPosted: Wed Aug 17, 2011 8:12 pm 
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Joined: Fri May 07, 2010 7:06 am
Posts: 906
If you want to get real part of the FFT, you should read output_array[i].x - it contains real part. Is it what you need?

P.S. As for donations - it is impossible to accept PayPal payments from Russia, unfortunately. If you want, you can e-mail me and tell specific sum you want to donate, and I will send you a link to the special webform used for non-standard payments. (I need to know payments sum and currency beforehand in order to prepare this form)


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 Post subject: Re: real part of fft
PostPosted: Sat Aug 20, 2011 3:26 pm 
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Joined: Wed Aug 17, 2011 10:56 am
Posts: 2
Sergey.Bochkanov wrote:
If you want to get real part of the FFT, you should read output_array[i].x - it contains real part. Is it what you need?

P.S. As for donations - it is impossible to accept PayPal payments from Russia, unfortunately. If you want, you can e-mail me and tell specific sum you want to donate, and I will send you a link to the special webform used for non-standard payments. (I need to know payments sum and currency beforehand in order to prepare this form)



Thank you very much for your answer it was indeed very simple.

I took my time because i wanted to be sure that i undestood before answering .

If i draw the "power spectrum" of the joint movement via the kinect sensor, therefore i can do:

n = total number of recordings ;

alglib.fftr1d(timeref, out freqref);

Powerspectrum = 2 * Math.Pow((Math.Sqrt(Math.Pow(freqref[i].x, 2) + Math.Pow(freqref[i].y, 2)) / n), 2)

Each frequency step = (n / total time)

If this is correct, are there any precautions that i should take with n? (should n be a power of 2 for example?)


2:)Concerning donation, it's not much just a way to say thank you, may i pm you for that?

3°) The final objective of my personal project (opensource) is to look for the stability of jointmotion, therefore i would like to use the Lyapunov Exponent to quantify stabilty. I didn' t find any c# library that could help me code that, do you have an advice?

EDITT: i saw that alglib can help for nearest neigboor and delay choosing, but i lack the method to go from that to LLE.

thanx in advance


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