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Re: Inflection Point Detection


From: Ben Abbott
Subject: Re: Inflection Point Detection
Date: Mon, 14 Mar 2011 21:34:30 -0400

On Mar 14, 2011, at 8:59 PM, aegreen wrote:

> Can't seem to figure this out but I assume it's a common problem.
> 
> I have a data set that contains an inflection point between two linear
> equations. For example producing a graph as follows:
> 
>  ^
>   |              /
> y |             /
>   |_______/
>   |
> <------------------> x
>   |
>   |
> 
> Has any one had success or knows of a technique to use octave to determine
> the inflection point in this line?
> 
> Thanks,
> 
> AG

One approach would be to use mkpp, ppder, and ppval. I haven't tested this, but 
...

        pp = mkpp (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)

Ben






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