Re: Inflection Point Detection

[aegreen]

bpabbott wrote:
> 
>       pp = spline (x,y);
>       pp2 = ppder (ppder (pp));
>       d2y_by_dx2 = ppval (pp2, x);
>       n = find (abs (d2y_by_dx2) == max (abs (d2y_by_dx2)));
>       x_inflection = x(n)
> 

Thanks Ben that works great!

I apologize though, typically my data though doesn't have such a discrete
inflection point as I had indicated in the above graph. Is there some way to
use a least squared approach with a piecewise function?

I have inserted an image of the data that I am trying to find an inflection
point in (blue) and the data after it's been filtered with a third order
butterworth filter with a cut off frequency of 0.1Hz, so that you can get an
idea of what I am trying to do.

This problem has been stumping me for months so any thoughts or suggestions
even would be really appreciated, since I understand this is a little
outside the realm of this forum.

http://octave.1599824.n4.nabble.com/file/n3357323/VE.jpeg 

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