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## Re: [Help-gsl] spectrogram analysis ?

**From**: |
Alex Lopes |

**Subject**: |
Re: [Help-gsl] spectrogram analysis ? |

**Date**: |
Tue, 10 Aug 2010 13:34:40 -0300 |

At Sat, 16 Jan 2010 17:07:14 +0100,
wally wrote:
>** **
>** A spline interpolation and its derivative on this data works nice .**
>** I presume the integration will also work to find the areas, but i do**
>** not know how to get the zeropoints from the 1st derivative "**
>** gsl_spline_eval_deriv" results to determine the peaks.**
>** **
>** How to find the zero points ? Is there a peakfinder on a dataset**
>** known ? Is there an example sourcecode known which handle this**
>** problem ?**
Hi Wally,
I've done exactly this in Matlab. After you get the first derivative you can
do the following (in Matlab commented code) to find the maximum and minimum
points:
//fx1 is a vector with the y values of the spline derivative.
fx1(fx1>0)=1;
fx1(fx1<=0)=0;
extrema = find(diff(fx1)~=0); // it will detect where the first derivative
changes its signal. The accuracy depends on the fx1 range and length.
Now, I'm trying to translate this code to C using gsl. I need a little help
to compute the derivative. Could you send me a little piece of code showing
how to do it?
Thank you very much,
--
Alex Lopes Pereira

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